Why so expensive (flight recorders)

[Jim Beckman]

> A simple (EW Microrecorder) is under $800. In todays
> money, an extra $20 for a badge flight is less than
> the round of beers you buy. 40 badge flights and you
> can buy a second one. Pretty soon, you hold a club
> meeting to decide what to buy next once there are
>enough
> recorders.

Again you're making the wrong comparison. The point
is that a Garmin Etrex costs a tenth of that, and can
provide just as secure a record for badge flights.
It's not much for navigation, but it will tell you
how far away you are from where you're going, and what
your ground speed is. Surely a Silver Badge attempt
doesn't require moving map capabilities, or extensive
computation power. There's something to be said for
encouraging the new XC pilot to keep his head up out
of the cockpit.

Sounds like P3 is making good progress on making this
all accepted.

Jim Beckman

[nimbusgb]

On 15 Feb, 13:58, Jim Beckman
> wrote:
> > A simple (EW Microrecorder) is under $800. In todays
>
> > money, an extra $20 for a badge flight is less than
> > the round of beers you buy. 40 badge flights and you
> > can buy a second one. Pretty soon, you hold a club
> > meeting to decide what to buy next once there are
> >enough
> > recorders.
>
> Again you're making the wrong comparison. The point
> is that a Garmin Etrex costs a tenth of that,

Because the market is 100000 times bigger than the entire secure
flight recorder market

> and can provide just as secure a record for badge flights.

Not even nearly

> It's not much for navigation, but it will tell you
> how far away you are from where you're going, and what
> your ground speed is.

Right

> Surely a Silver Badge attempt
> doesn't require moving map capabilities, or extensive
> computation power. There's something to be said for
> encouraging the new XC pilot to keep his head up out
> of the cockpit.

Absolutely. In fact most clubs will insist you do the 50k with a map
not a GPS

>
> Sounds like P3 is making good progress on making this
> all accepted.
>
> Jim Beckman

The cost of GPS engines has dropped to the 20 dollar mark
The cost of memory is negligable
The cost of the analog section ( altimeter ) is a little more but not
massive.

You are paying for the small market you are in. Don't begrudge the few
manufacturers a profit on these devices. Its not as if they are all
buying themselves EB 28's on the profits. I developed a secure logger
when the system first got going but there was simply not enough money
in it for it to be a viable business. Nothing more than hand-to-mouth.

I could get my system going again and the component build cost would
be around £125. I can tell you that at a selling price of £500 it
still wouldnt be a business!

[Papa3]

On Feb 15, 9:09*am, nimbusgb >

[Jim wrote: and can provide just as secure a record for badge
flights]
>
[Ian wrote: Not even nearly]

Okay Ian - prove it. Prove that a COTS unit governed under the
manual OO procedures I've laid out in the referenced link doesn't
provide an equivalent level of security. Come on, I dare ya :-)


http://home.netcom.com/~pappa3/files/COTS/cots_security_draft.pdf

[nimbusgb]

On 15 Feb, 21:08, Papa3 > wrote:
> On Feb 15, 9:09 am, nimbusgb >
>
> [Jim wrote: and can provide just as secure a record for badge
>
> flights]
>
>
>
> [Ian wrote: Not even nearly]
>
> Okay Ian - prove it. Prove that a COTS unit governed under the
> manual OO procedures I've laid out in the referenced link doesn't
> provide an equivalent level of security. Come on, I dare ya :-)
>
> http://home.netcom.com/~pappa3/files/COTS/cots_security_draft.pdf

A cots GPS is still not as secure as an IGC logger.

Your presentation appears to have merit and I'd support using it for
badges.

Ian

[Papa3]

On Feb 16, 7:45*am, nimbusgb > wrote:
> On 15 Feb, 21:08, Papa3 > wrote:
>
> > On Feb 15, 9:09 am, nimbusgb >
>
> > [Jim wrote: * and can provide just as secure a record for badge
>
> > flights]
>
> > [Ian wrote: * Not even nearly]
>
> > Okay Ian - prove it. * Prove that a COTS unit governed under the
> > manual OO procedures I've laid out in the referenced link doesn't
> > provide an equivalent level of security. *Come on, I dare ya *:-)
>
> >http://home.netcom.com/~pappa3/files/COTS/cots_security_draft.pdf
>
> A cots GPS is still not as secure as an IGC logger.
>
> Your presentation appears to have merit and I'd support using it for
> badges.
>
> Ian

"Not as secure..." Why? Specifics. Specifics. I have yet to
hear anyone make a specific argument. Generalities, yes, but
specifics, no.

I'm not trying to stand up on a soapbox here. However, I do expect
folks to do a little more than just spout the "conventional wisdom"
without a little more thought or work going into it. I'll make it
easier on folks. What specific security threats are there which fall
in the realm of reasonable probability:

- Most likely: Someone downloads a log file from a COTS logger and
alters the file using a text editor to fix a height penalty, tweak a
few fixes by a couple of feet to get into an OZ, etc. It turns out
that there a number of low tech and medium tech solutions to this:
* Lowest tech: Seal off any data ports and only allow downloading
and analysis of the file under the supervision of the OO. Very low
tech. Very high security.
* Medium tech: Rely on the encyrption provided by third party tools
such as G72Win or SeeYou. Could someone with access to a Cray
supercomputer for a few hours break their encryption methodology?
Sure. Does it matter as long as the OO takes control of the file
immediately upon download? No.

- Less likely: Someone manufactures a log on their PC using Condor
and SeeYou and loads it up to the logger before a flight. Solutions:
* Very Low Tech: Inspection of the logger to ensure memory is empty
prior to flight. Very easy to do since COTS loggers inherently
provide the ability to manage log files through their UI.
* Medium Tech: Rely on the inherent feature of (some) loggers which
zero out the timestamps of any files loaded into memory which are not
generated by the GPS itself.

- Unlikely: Pilot manipulates the datum in flight (have heard this
one spouted a lot). Has anyone actually looked at what would
happen? Depending on which datums are swapped, the impact is
somewhere between a few hundred meters and ... well a lot of
kilometers. Post flight analysis will pick this up in a heartbeat,
as the glider will have an instantaneous velocity approaching that of
the Starship Enterprise. This is much different than a single
spurios fix or group of dropped fixes where the smoothed average is
highly believable. I can show a trace of this if anyone wants to see
it.

Point being, it's easy to talk about this in vague terms, but when you
put your mind to it, it turns out that there's not that much which
would be required to make a very secure log file for the purpose of
supervised badge flights.

All good stuff to be pondering as we in the Northern Hemisphere await
the return of soaring season.

P3

[nimbusgb]

On 16 Feb, 12:45, nimbusgb > wrote:
> On 15 Feb, 21:08, Papa3 > wrote:
>
> > On Feb 15, 9:09 am, nimbusgb >
>
> > [Jim wrote: and can provide just as secure a record for badge
>
> > flights]
>
> > [Ian wrote: Not even nearly]
>
> > Okay Ian - prove it. Prove that a COTS unit governed under the
> > manual OO procedures I've laid out in the referenced link doesn't
> > provide an equivalent level of security. Come on, I dare ya :-)
>
> >http://home.netcom.com/~pappa3/files/COTS/cots_security_draft.pdf
>
> A cots GPS is still not as secure as an IGC logger.
>
> Your presentation appears to have merit and I'd support using it for
> badges.
>
> Ian

Ho boy!

It is VERY simple to split the casing on COTS units and substitute
some internal microprocessor controlled gubbins or even reprogram the
software so that it appears to perform like the real thing but given a
few 'special' keystrokes could do just about anything, including
dumping some prerecorded track or trace. I have a Garmin 12 that I put
a NiMh pack into with a charger circuit INSIDE the casing.

Without the manufacurers PKI key it would be extremely difficult to
acheive this sot of thing with an IGC logger and still avoid detection
using the VALI programs.

That's why a COTS unit is not as secure. There is no way for anyone to
check the validity of what's being produced from the unit or whether
the unit is still a 'standard' cots unit.

Now if you want to talk about how #probable# it is that someone is
going to spend time, money and effort in replacing the internals of a
cots unit just toe get a diamond height, thats another argument. Its
MUCH quicker and simpler to just go find some wave somewhere.

This was all argued out more than 10 years ago!

Ian

[Papa3]

On Feb 16, 12:38*pm, nimbusgb > wrote:
> On 16 Feb, 12:45, nimbusgb > wrote:
>
>
>
>
>
> > On 15 Feb, 21:08, Papa3 > wrote:
>
> > > On Feb 15, 9:09 am, nimbusgb >
>
> > > [Jim wrote: * and can provide just as secure a record for badge
>
> > > flights]
>
> > > [Ian wrote: * Not even nearly]
>
> > > Okay Ian - prove it. * Prove that a COTS unit governed under the
> > > manual OO procedures I've laid out in the referenced link doesn't
> > > provide an equivalent level of security. *Come on, I dare ya *:-)
>
> > >http://home.netcom.com/~pappa3/files/COTS/cots_security_draft.pdf
>
> > A cots GPS is still not as secure as an IGC logger.
>
> > Your presentation appears to have merit and I'd support using it for
> > badges.
>
> > Ian
>
> Ho boy!
>
> It is VERY simple to split the casing on COTS units and substitute
> some internal microprocessor controlled gubbins or even reprogram the
> software so that it appears to perform like the real thing but given a
> few 'special' keystrokes could do just about anything, including
> dumping some prerecorded track or trace. I have a Garmin 12 that I put
> a NiMh pack into with a charger circuit INSIDE the casing.
>
> Without the manufacurers PKI key it would be extremely difficult to
> acheive this sot of thing with an IGC logger and still avoid detection
> using the VALI programs.
>
> That's why a COTS unit is not as secure. There is no way for anyone to
> check the validity of what's being produced from the unit or whether
> the unit is still a 'standard' cots unit.
>
> Now if you want to talk about how #probable# it is that someone is
> going to spend time, money and effort in replacing the internals of a
> cots unit just toe get a diamond height, thats another argument. Its
> MUCH quicker and simpler to just go find some wave somewhere.
>
> This was all argued out more than 10 years ago!
>
> Ian- Hide quoted text -
>
> - Show quoted text -


Unfortunately, it was argued out by people who didn't take the time to
talk with the manufacturers of the COTS units themselves!! The
statement that " it would be It is VERY simple to split the casing on
COTS units and substitute
some internal microprocessor controlled gubbins or even reprogram the
software so that it appears to perform like the real thing but given a
few 'special' keystrokes could do just about anything, including
dumping some prerecorded track or trace" neglects the fact that a
company like Garmin or Magellan is more than a little sensitive about
people reverse-engineering their products. Show me somebody who's
rebuilt their Garmin 76 as you describe, and I'll believe you. I have
detailed correspondence with Garmin engineers willing to discuss the
issue.

Of course, there are more than a few people out there (myself
included) who know how to open the case of a number of IGC Approved
Secure loggers to defeat the tamper switch. Gasp! On one of the
units I own, this was precipitated by having to replace the small
backup battery which preserves memory. Once opened and accidentally
disconnected from the power supply, the security seal is broken.
What to do? Oh, need to send the unit back to the manufacturer to
reset the code. But, as long as I have it open, let's see how this
works. Ahah, here's the mechanical switch. Let's see now, where
does this come in contact with the case? Let's just mark that point
on the case for "future reference". Now, send it back to the
manufacturer and the unit comes back as "secure." Of course, now
that I know exactly where the switch is and how to defeat that...
Where did I put that 1/8" drill bit...

And off we go. Of course, why stop with cracking the case. I'm
sure any firmware guru and EE who wants to go to the effort of hacking
a COTS GPS can more easily create a low power GPS signal generator
which can spoof GPS signals with off-the-shelf components. In fact,
my firm works with a number of freight/transportation firms on RFID,
GPS, and other tracking technologies. Guess what one of the very REAL
threats they're facing is right now - GPS spoofing. See for
example:

http://www.eyefortransport.com/index.asp?news=38732&nli=freight&ch

Anyone who believes that an IGC Approved Recorder is somehow
"significantly more" secure from tampering by a sophisticated/
dedicated cheater is fooling him/herself. I strongly agree that the
IGC Approved Recorder provides a valuable solution for non-supervised/
minimally supervised flights. The overhead associated with having to
manually review every recorder at a large contest would be a
nightmare. But, could a dedicated cheater defeat security on an IGC
Approved Logger. Yup.

So, before we go off into fantasy land, let's start talking about the
REALISTIC threats and the differences between the two approaches.
IGC Approved loggers clearly have the advantage in that they offer an
easier administrative approach at contests and other gatherings where
there isn't direct supervision of the FRs. COTS loggers will
require additional manual intervention which make them less attractive
for those situations, but they are equally desirable for a supervised
Silver C.

Off to go skiing. At least I'll be on the ridge...

P3

[nimbusgb]

> So, before we go off into fantasy land, let's start talking about the
> REALISTIC threats and the differences between the two approaches.
> IGC Approved loggers clearly have the advantage in that they offer an
> easier administrative approach at contests and other gatherings where
> there isn't direct supervision of the FRs. COTS loggers will
> require additional manual intervention which make them less attractive
> for those situations, but they are equally desirable for a supervised
> Silver C.
>
> Off to go skiing. At least I'll be on the ridge...
>
> P3

So we agree then!

[PCool]

I fly in Italy, and Garmin COTS are accepted for badges up to gold,
excluding the heigth (1000 and 3000 m).
For diamonds and 1000m, 3000m, 5000m you need an approved IGC logger.

Once you understand that COTS can be manipulated anytime without even
bothering touching the hardware, you also understand that an IGC approved
recorder cannot even be tampered and leaves no doubts about the flight.

If we consider a COTS like a camera, then it all comes down to the
observation of a judge/supervisor just like with cameras in the good old
times. Fact is, that there are too many COTS and unless there are some
restrictions on models we cannot expect that a man is able to know and
understand each of them. So there has to be a "white list" and a "black
list".

I fly with Garmin 76S and 76CSX. Like all Garmin models they cannot be
hacked. There's no way one can change the firmware, otherwise one could also
load pirated maps and everybody know that with Garmin it's impossible on
COTS unless you have an unlock code. The newer Colorado 400T has glide
calculations as well and seems to be the only valid alternatives to palms at
least for basic data and good maps.

However, with garmins you can save a flight and then load it back as the
current track. Or you can load a track and then put it on as the current
track. Not that this means anything, cause the track should be coherent to
the flight times which you cannot predict.

Personally I think that COTS are ok for most of the times, even in
competitions if a competent supervisor is on the field.

Paul


"nimbusgb" > ha scritto nel messaggio
...
>
>> So, before we go off into fantasy land, let's start talking about the
>> REALISTIC threats and the differences between the two approaches.
>> IGC Approved loggers clearly have the advantage in that they offer an
>> easier administrative approach at contests and other gatherings where
>> there isn't direct supervision of the FRs. COTS loggers will
>> require additional manual intervention which make them less attractive
>> for those situations, but they are equally desirable for a supervised
>> Silver C.
>>
>> Off to go skiing. At least I'll be on the ridge...
>>
>> P3
>
> So we agree then!

[nimbusgb]

>
> I fly with Garmin 76S and 76CSX. Like all Garmin models they cannot be
> hacked.

Yes they can. Garmin tends to use industry standard processors and
components in their units so there's no reason why they couldnt be
hacked if there was something in it for someone.They use flash memory
for their code, they have serial uploaders to facilitate flashing new
updates. The fact that they haven't been hacked is simply because
there is no reason to hack them!

[PCool]

No they can't, and they never have been hacked in 10 years. There's a huge
business on Garmin for travelling. While all navigators like tomtom, MIO,
etc. have been hacked (and you can upload maps to them and even change the
operating system- like for MIO) there has never been a single unique case of
someone that could break Garmin's algorithms for uploading a stupid map to
the device (their maps of course. there are also public maps).

Anything can be done of course. Even swapping the internal hardware with
another thing. But then you can also build a fake LX Colibrì as well.
There are more reasons to hack a garmin than to hack an LX, believe me.
Garmin maps costs hundreds of dollars. It's a huge business and you will not
find a single hacked map on the whole internet. If you can't upload a garmin
map without their code I let you imagine how difficult it is to hack the
firmware. The fact that they haven't been hacked is simply because it is
too difficult, and that's something going on since the end of the 90s! (To
be precise, there exists a software that allows you to change the welcome
text screen, and that's all).

Garmin's policy is that for each device you have to buy separately new maps,
or better a new unlock code for each device, at the full price. Europe's
maps costs more than a TomTom hardware+maps ! People nevertheless buy also
Garmin because they are simply the best around.

I compiled custom "extra" maps for garmin devices, topo maps, airports,
airspace etc for the Alps, making a Garmin screen more or less similar to
SeeYou mobile moving map using the "unofficial" cgpsmapper software (which I
paid for) so though I don't consider myself an expert on their firmware, at
least I can say that I spent some hundreds hours working on those devices.




"nimbusgb" > ha scritto nel messaggio
...
>
>>
>> I fly with Garmin 76S and 76CSX. Like all Garmin models they cannot be
>> hacked.
>
> Yes they can. Garmin tends to use industry standard processors and
> components in their units so there's no reason why they couldnt be
> hacked if there was something in it for someone.They use flash memory
> for their code, they have serial uploaders to facilitate flashing new
> updates. The fact that they haven't been hacked is simply because
> there is no reason to hack them!
>

[Tony Burton]

One of the restrictions on the use of COTS units for Silver and Gold badge flights (assuming that
their use is approved at the upcoming IGC annual meeting), is that units that have a dead reckoning
function on loss of signal may be used unless the function can be disabled. I have been hold that
Garmin units have this function but that it cannot be disabled, which would disqualify them. Does
anyone have any facts on this?

[PCool]

Tony this is something I also heard of.
I use Garmins and when signal is lost it says "signal lost". That's it. When
I enter a tunnel it says "signal lost" within 3 seconds.
Same happens on SirfIII chipsets. Even if a device interpolates a signal
between two known points in a period of a few second, that's a straight line
and I can't see what kind of advantage it could hold. I say "a few seconds",
cause after a few seconds if signal is lost it is lost! And that's for sure.
Garmin and modern GPS chipsets are much more accurate and reliable then
older chipset used inside (f.i.) LX.
I have seen (and can demonstrate) logs by LX-20 that show a standard Cirrus
flying at almost 800km/h (like a Boeing 737).
Expecially while banking at 45 degrees these devices (old chipsets) tend to
loose signal and the firmware (gps firmware) sends incorrect data. This is a
statement, it's logged. You can see a glider jumping like a rabbit with
10-15km steps!
So what is the point with interpolation on a straight line (if at all it is
done, I do not any evidence of this) in 2-3 seconds?
At least a Garmin will always report correct coordinates. I suspect many old
LX do not in certain circumstances. Fact is that IGC is not declaring these
devices unreliable. (clearly I talk about LX but generally I guess any
other device with some 8-10 years life).
So if it is not important that official loggers are precise, I can't
understand why a COTS should - given the fact that all evidences show that
newer chipsets are times more accurate then older.

The only issue should be that a garmin can be "tampered" (theoretically),
while an official flight recorder cannot.
So use a COTS under supervision of an officer and that's all (just like with
cameras).

I think that it is time that someone at IGC take in consideration what
pilots say, and not only what IGC approved manufacturers want and say.



"Tony Burton" > ha scritto nel messaggio
...
> One of the restrictions on the use of COTS units for Silver and Gold badge
> flights (assuming that
> their use is approved at the upcoming IGC annual meeting), is that units
> that have a dead reckoning
> function on loss of signal may be used unless the function can be
> disabled. I have been hold that
> Garmin units have this function but that it cannot be disabled, which
> would disqualify them. Does
> anyone have any facts on this?

[nimbusgb]

>
> I think that it is time that someone at IGC take in consideration what
> pilots say, and not only what IGC approved manufacturers want and say.
>

Everyone involved at the IGC is very firmly connected to gliding and,
knowing more than one or two of them, I can say all of them have the
sports best interests at heart. Trying to make things workable on a
global scale and still have some level of security when an OO is not
about was a very difficult task. With 20:20 hindsight it may be easy
to say they did not get it perfect but they came up with a workable
system.

At the time that flight recorders were just getting going a LOT of
consultation was done and many, many hours were spent by people like
Tim for zero reward apart from delivering an acceptable methodology
for improving and simplifying the flight verification procedures. At
the time Cambridge were the only manufacturers of any sort of flight
recorder following their early demos in Sweden in 93 and New Zealand
in 95. Even they did not get things all their way in the ensuing
regulation changes. In this day and age and the track record of
American companies it still surprises me that they didn't tie the
whole idea up in patents which might have had us paying 5 times the
current price for flight recorders today.

I agree that the communication to and consultation with the membership
appears to be very poor at times but I don't see too many people
sticking their heads above the parapet to try to change that. Perhaps
they are all too aware they they will become targets for bored pilots!

[PCool]

I agree with you, but I would like to point that 1993 is 15 years ago.
Technology has changed a lot, so the methodology has to be
adapted a little bit.
>In this day and age and the track record of
> American companies it still surprises me that they didn't tie the
> whole idea up in patents which might have had us paying 5 times the
> current price for flight recorders today.

No one would buy a flight recorder so expensive, that's why. People on this
group claim that loggers are already too expensive.
If you see a logger from the specs point of view, and the investments they
did in order to fulfill these specs, they are not too expensive. If you
instead look at their mere functionalities, then it looks like they are way
too expensive.

After all, it's just a matter of considering a COTS gps just like a camera
and revise the checking procedures and the supervision duties.
Actually it all comes down to the point that an approved GPS cannot be
modified and reports the truth. Let's leave it like that.
Let's at the same point replace the old cameras with COTS.
Mainly because a COTS gps is useful for flying and not only for recording
data.

In any case, if there is no supervision (an officer, or whatever) it's clear
that the only choice is (for me) a nice Colibri by LX, which works like a
charm.




"nimbusgb" > ha scritto nel messaggio
...
> >
>> I think that it is time that someone at IGC take in consideration what
>> pilots say, and not only what IGC approved manufacturers want and say.
>>
>
> Everyone involved at the IGC is very firmly connected to gliding and,
> knowing more than one or two of them, I can say all of them have the
> sports best interests at heart. Trying to make things workable on a
> global scale and still have some level of security when an OO is not
> about was a very difficult task. With 20:20 hindsight it may be easy
> to say they did not get it perfect but they came up with a workable
> system.
>
> At the time that flight recorders were just getting going a LOT of
> consultation was done and many, many hours were spent by people like
> Tim for zero reward apart from delivering an acceptable methodology
> for improving and simplifying the flight verification procedures. At
> the time Cambridge were the only manufacturers of any sort of flight
> recorder following their early demos in Sweden in 93 and New Zealand
> in 95. Even they did not get things all their way in the ensuing
> regulation changes. In this day and age and the track record of
> American companies it still surprises me that they didn't tie the
> whole idea up in patents which might have had us paying 5 times the
> current price for flight recorders today.
>
> I agree that the communication to and consultation with the membership
> appears to be very poor at times but I don't see too many people
> sticking their heads above the parapet to try to change that. Perhaps
> they are all too aware they they will become targets for bored pilots!

[Papa3]

On Feb 20, 3:39*pm, nimbusgb > wrote:
>
> Everyone involved at the IGC is very firmly connected to gliding and,
> knowing more than one or two of them, I can say all of them have the
> sports best interests at heart. Trying to make things workable on a
> global scale and still have some level of security when an OO is not
> about was a very difficult task. With 20:20 hindsight it may be easy
> to say they did not get it perfect but they came up with a workable
> system.
>
> At the time that flight recorders were just getting going a LOT of
> consultation was done and many, many hours were spent by people like
> Tim for zero reward apart from delivering an acceptable methodology
> for improving and simplifying the flight verification procedures. At
> the time Cambridge were the only manufacturers of any sort of flight
> recorder following their early demos in Sweden in 93 and New Zealand
> in 95. Even they did not get things all their way in the ensuing
> regulation changes. In this day and age and the track record of
> American companies it still surprises me that they didn't tie the
> whole idea up in patents which might have had us paying 5 times the
> current price for flight recorders today.
>
> I agree that the communication to and consultation with the membership
> appears to be very poor at times but I don't see too many people
> sticking their heads above the parapet to try to change that. Perhaps
> they are all too aware they they will become targets for bored pilots!


A very rational post. I have to admit that I was one of the folks who
was a strident (if under-informed) critic of folks on the GFAC when I
first got involved in the issue. I personally feel badly about that,
and I would hope that most of us now realize it's a thankless job.
In large part, I agree that the IGC and GFAC got it about right,
especially the part about establishing standard record formats which
allow us to speak the same language when it comes to log file analysis
and the like. Many commercial industries continue to struggle with
this even today.

OTOH, I have to at least suggest that the GFAC has tended (if
unintentionally) to represent the views of certain regions where the
conduct of gliding is highly organized and revolves around reasonably
well equipped clubs. The sense of frustration felt by the grass
roots in other locations seems irrational to them; a sort of
cognitive-dissonance if you will. Couple that with the fact that
communication has not always been especially open, consistent or
complete (in today's world we'd use the buzz-word "transparent") and
it's not hard to understand why there have been some harsh critics.

If you look at COTS, it would have been nice if the attitude going in
had been "how can we make this work" as opposed to "why won't this
work". Just that change in mindset would have quickly led to a
solution-driven approach which would have moved the entire effort
along much faster. Couple that with a more open/transparent
communication plan (think along the lines of an open-source movement
with issues being identified and then addressed by the community), and
I'm convinced we would already be using COTS equipment successfully
for badge flights. So, if anything, it may be that poor governance
has been the issue, and it's not too late to change that.

Respectfully,
Erik Mann
LS8-18 (P3)

[Marc Ramsey[_2_]]

Papa3 wrote:
> OTOH, I have to at least suggest that the GFAC has tended (if
> unintentionally) to represent the views of certain regions where the
> conduct of gliding is highly organized and revolves around reasonably
> well equipped clubs. The sense of frustration felt by the grass
> roots in other locations seems irrational to them; a sort of
> cognitive-dissonance if you will. Couple that with the fact that
> communication has not always been especially open, consistent or
> complete (in today's world we'd use the buzz-word "transparent") and
> it's not hard to understand why there have been some harsh critics.

The "grass roots" view is certainly represented, I've never been a
member of a highly organized, well-equipped club. ;)

I'm not sure how much more transparent GFAC can be, ask a question here,
or send a private email to one of the members, and you'll get an answer.
You may not like the answer, but that is a different issue.
Obviously, we deal with manufacturer proprietary information during the
approval process, and that can't be publicly discussed. But, everything
else is open, and always has been.

> If you look at COTS, it would have been nice if the attitude going in
> had been "how can we make this work" as opposed to "why won't this
> work". Just that change in mindset would have quickly led to a
> solution-driven approach which would have moved the entire effort
> along much faster. Couple that with a more open/transparent
> communication plan (think along the lines of an open-source movement
> with issues being identified and then addressed by the community), and
> I'm convinced we would already be using COTS equipment successfully
> for badge flights. So, if anything, it may be that poor governance
> has been the issue, and it's not too late to change that.

GFAC is a technical committee, not a policy or rules committee. There
are those of us (like myself) who believe allowing COTS GPS would be
good policy under the right circumstances, and those who don't. But,
from a technical standpoint, there are certain things we have to point
out, like the lack of pressure altitude recording capability, and the
significant differences in functionality, performance, and security
provided by units from various manufacturers.

The IGC (not GFAC) has always been the appropriate place to initiate
this proposal. The fact that the last proposal submitted to the IGC did
a rather poor job of addressing certain important technical and policy
issues is what slowed down the process.

At the next IGC Plenary Meeting (29 February through 1 March), there
will be a specific proposal from the IGC Sporting Code Committee to
change SC3 to allow use of COTS GPS in conjunction with barographs for
Silver and Gold badges. May I, once again, suggest that you contact
your IGC delegate to make your viewpoint known?

Marc

[Ian[_2_]]

On Thu, 21 Feb 2008 18:42:11 +0000, Marc Ramsey wrote:

> At the next IGC Plenary Meeting (29 February through 1 March), there
> will be a specific proposal from the IGC Sporting Code Committee to
> change SC3 to allow use of COTS GPS in conjunction with barographs for
> Silver and Gold badges. May I, once again, suggest that you contact
> your IGC delegate to make your viewpoint known?

Why bother with the barographs?

For the purposes of establishing that the pilot met the requirements for
a silver or gold height gain, surely GPS altitude is adequate?
(Particularly now that "SA" has been discontinued). On OLC there are
many, many log files with both GPS and barometric altitude. The GPS
altitudes are different, but they are not unreasonable and they are not
consistently "less accurate" than pressure altitudes.

Yes, they are different - GPS alitude is a different parameter to
pressure altitude. Yes the current Sporting Code requires us to measure
altitude with pressure instruments, but that is a legacy from a time when
we had no alternative.

If a pilot has achieved a height gain of 1000m or 3000m as measured with
a COTS GPS altitude (controlled by an OO), can we not acknowledge that he
as accomplished a significant achievement, give him a pat on the back and
pin a badge on his chest? This is the 21st century after all if you going
to change the rules, then lets do it properly.

If you are worried about "rogue" GPS readings (as might be caused by GPS
failure, poor reception or jamming), give the OO or the national body the
option of throwing out any GPS points that are totally unrealistic.

I presume that GPS altitude will be accepted for proving the requirement
of flight continuity on distance flights - please don't tell me that this
is not true - surely there is no valid reason to turn this down.

Far too many badges have gone unclaimed simply because aspiring pilots
have been frustrated by the requirement to borrow or buy the dinosaur
equipment required by the IGC to verify the performance.

Yes, secure flight records have their place. But for too long, the few
pilots who actually need them have been subsidized by forcing many whose
sporting objectives are more modest help pay for the R&D.

Our sport is slowly dying, not at the top levels, but at the grass root
levels. Why? Because there are so many obstacles to frustrate upcoming
pilots - it is just not as much fun for today's youth as it was for the
many of us first took up the sport 25 years ago. Now there is a chance to
get rid of one of those obstacles, lets ditch the barographs!


Ian

[Marc Ramsey[_2_]]

Ian wrote:
> On Thu, 21 Feb 2008 18:42:11 +0000, Marc Ramsey wrote:
>
>> At the next IGC Plenary Meeting (29 February through 1 March), there
>> will be a specific proposal from the IGC Sporting Code Committee to
>> change SC3 to allow use of COTS GPS in conjunction with barographs for
>> Silver and Gold badges. May I, once again, suggest that you contact
>> your IGC delegate to make your viewpoint known?
>
> Why bother with the barographs?

It's rather simple, GPS altitude is not currently an IGC recognized
means of measuring altitude in soaring performances, and changing that
is far more complex than adding COTS GPS as an alternate means of
documenting position evidence.

Marc

[toad]

On Feb 21, 6:25 pm, Marc Ramsey > wrote:
> Ian wrote:
> > On Thu, 21 Feb 2008 18:42:11 +0000, Marc Ramsey wrote:
>
> >> At the next IGC Plenary Meeting (29 February through 1 March), there
> >> will be a specific proposal from the IGC Sporting Code Committee to
> >> change SC3 to allow use of COTS GPS in conjunction with barographs for
> >> Silver and Gold badges. May I, once again, suggest that you contact
> >> your IGC delegate to make your viewpoint known?
>
> > Why bother with the barographs?
>
> It's rather simple, GPS altitude is not currently an IGC recognized
> means of measuring altitude in soaring performances, and changing that
> is far more complex than adding COTS GPS as an alternate means of
> documenting position evidence.
>
> Marc

And what is so complicated in adding GPS altitiude as an IGC
recognized measurement ? Especially since GPS lat,lon is a
recognized. I am serious, please tell me.

Todd Smith
3S

[PCool]

This http://www.gpsinformation.net/main/altitude.htm guy (7 years ago) says
that accuracy was +-40 meters, but with DGPS should improve to +-10m (what
we should have now.).

This http://www.scottkurowski.com/flying.htm#accuracy made accurate
calculation on precisions, coming to +-7 feet precision in 2006 (?) with a
garmin 296.

These http://docs.controlvision.com/pages/gps_altimetry.php people say in
2004 that there is a bug in most of cheap gps chips that make altitude
calculation wrong by +-200 feet, and why it happens.

Most trekking gps have a baro sensor to compensate and calibrate gps
altitude nowadays (garmin for all S serie).





"toad" > ha scritto nel messaggio
...
> On Feb 21, 6:25 pm, Marc Ramsey > wrote:
>> Ian wrote:
>> > On Thu, 21 Feb 2008 18:42:11 +0000, Marc Ramsey wrote:
>>
>> >> At the next IGC Plenary Meeting (29 February through 1 March), there
>> >> will be a specific proposal from the IGC Sporting Code Committee to
>> >> change SC3 to allow use of COTS GPS in conjunction with barographs for
>> >> Silver and Gold badges. May I, once again, suggest that you contact
>> >> your IGC delegate to make your viewpoint known?
>>
>> > Why bother with the barographs?
>>
>> It's rather simple, GPS altitude is not currently an IGC recognized
>> means of measuring altitude in soaring performances, and changing that
>> is far more complex than adding COTS GPS as an alternate means of
>> documenting position evidence.
>>
>> Marc
>
> And what is so complicated in adding GPS altitiude as an IGC
> recognized measurement ? Especially since GPS lat,lon is a
> recognized. I am serious, please tell me.
>
> Todd Smith
> 3S

[Marc Ramsey]

toad wrote:
> On Feb 21, 6:25 pm, Marc Ramsey > wrote:
>> It's rather simple, GPS altitude is not currently an IGC recognized
>> means of measuring altitude in soaring performances, and changing that
>> is far more complex than adding COTS GPS as an alternate means of
>> documenting position evidence.
>
> And what is so complicated in adding GPS altitiude as an IGC
> recognized measurement ? Especially since GPS lat,lon is a
> recognized. I am serious, please tell me.
>

GPS altitude and pressure altitude measure two distinct concepts which
happen to use the same units. Conversion between the two is an
approximation requiring both local sounding data and agreement on use of
a specific set of formulas. The IGC has been using pressure altitude
almost exclusively for quite some time, and will continue to do so for a
variety of reasons. These ease of comparability with past flight
performances and records, the need to detect incursions into airspace
defined by pressure altitude limits, collection of redundant altitude
data for security and reliability, and general bureaucratic inertia.
While there is provision in the Sporting Code for optical and radar
altitude measurements (which are more closely related to GPS altitude),
other requirements pretty much eliminate the possibility of actual use,
and if someone managed to find a legitimate way, the conversion would
have to be handled on a case specific basis. I'm aware of two efforts
in recent years to amend the Sporting Code to allow for use of geometric
altitude (GPS, radar, optical) in certain circumstances, neither
proposal got very far.

Latitude and longitude do not suffer from these problems. The only real
issue is the datum used, IGC approved flight recorders always use a
specific datum, and conversion to/from other datums used to locate photo
turnpoints, ground observers, etc., can be done using well understood
transformations often backed by international standards.

Tying the COTS GPS rules to the use of GPS altitude would almost
certainly result in failure to pass the proposal. Requiring use of a
pressure altitude recording device (i.e. barograph) increases the
probability that a majority of the IGC delegates will vote in favor of
the proposal. That's politics for you...

Marc

[Ian[_2_]]

On Fri, 22 Feb 2008 09:39:06 -0800, Marc Ramsey wrote:

> GPS altitude and pressure altitude measure two distinct concepts which
> happen to use the same units. Conversion between the two is an
> approximation requiring both local sounding data and agreement on use of
> a specific set of formulas. The IGC has been using pressure altitude
> almost exclusively for quite some time, and will continue to do so for a
> variety of reasons. These ease of comparability with past flight
> performances and records, the need to detect incursions into airspace
> defined by pressure altitude limits, collection of redundant altitude
> data for security and reliability, and general bureaucratic inertia.
> While there is provision in the Sporting Code for optical and radar
> altitude measurements (which are more closely related to GPS altitude),
> other requirements pretty much eliminate the possibility of actual use,
> and if someone managed to find a legitimate way, the conversion would
> have to be handled on a case specific basis.

None of this has provides any good reason why a badge for silver or gold
height gain should not be awarded on the basis of height gain measured by
means of GPS altitude instead of barometric pressure altitude.

Both GPS and pressure altitude are subject to errors and pressure
altitude is not necessarily the more accurate. Two performances by
different pilots on different days in different weather, both providing
equal height gain measured by pressure altitude does not imply that the
two gliders actually achieved the same height gain if could be measured
with a tape measure. Just the same if one performance had been measured
with GPS altitude. But both performances would be an excellent
demonstration of pilot skills and worthy of recognition with the
appropriate badge!

This may not be 100% "fair". But a distance performance navigated with a
compass and map and measured with turn point photographs is a more
difficult achievement than the same task navigated with GPS and measured
with a Flight Recorder. You have to fly further to get a decent photo and
the cockpit workload is significantly higher. Yet we award the same badge
for both performances - thus some "unfairness" already exists in the code.

> Tying the COTS GPS rules to the use of GPS altitude would almost
> certainly result in failure to pass the proposal. Requiring use of a
> pressure altitude recording device (i.e. barograph) increases the
> probability that a majority of the IGC delegates will vote in favor of
> the proposal. That's politics for you...

This political argument sounds far more plausible than any technical one.
I would like to see a list of IGC delegates (identified by country) who
are apposed to the use of GPS altitude to measure height gain. Then we
could explain to them that their attitude is quietly killing our sport...

To put it another way, if we accept COTS GPS together with COTS altitude,
then overnight there would be 10000 Flarm equipped gliders which would
each have their own dedicated Flight Recorder at no additional cost at
all... Now that would be a powerful boost for our sport.


Ian

[Marc Ramsey]

Ian wrote:
> On Fri, 22 Feb 2008 09:39:06 -0800, Marc Ramsey wrote:
>
>> GPS altitude and pressure altitude measure two distinct concepts which
>> happen to use the same units. Conversion between the two is an
>> approximation requiring both local sounding data and agreement on use of
>> a specific set of formulas. The IGC has been using pressure altitude
>> almost exclusively for quite some time, and will continue to do so for a
>> variety of reasons. These ease of comparability with past flight
>> performances and records, the need to detect incursions into airspace
>> defined by pressure altitude limits, collection of redundant altitude
>> data for security and reliability, and general bureaucratic inertia.
>> While there is provision in the Sporting Code for optical and radar
>> altitude measurements (which are more closely related to GPS altitude),
>> other requirements pretty much eliminate the possibility of actual use,
>> and if someone managed to find a legitimate way, the conversion would
>> have to be handled on a case specific basis.
>
> None of this has provides any good reason why a badge for silver or gold
> height gain should not be awarded on the basis of height gain measured by
> means of GPS altitude instead of barometric pressure altitude.

You may not like the answer, but the IGC measures height gains, loss of
height, etc., using pressure altitude. You are welcome to contact your
IGC delegate and indicate you would like this to change.

> Both GPS and pressure altitude are subject to errors and pressure
> altitude is not necessarily the more accurate. Two performances by
> different pilots on different days in different weather, both providing
> equal height gain measured by pressure altitude does not imply that the
> two gliders actually achieved the same height gain if could be measured
> with a tape measure. Just the same if one performance had been measured
> with GPS altitude. But both performances would be an excellent
> demonstration of pilot skills and worthy of recognition with the
> appropriate badge!

The altitudes measured by the IGC are not the same as heights measured
by tape measure, GPS, etc. You are effectively comparing apples and,
uh, pears.

> This may not be 100% "fair". But a distance performance navigated with a
> compass and map and measured with turn point photographs is a more
> difficult achievement than the same task navigated with GPS and measured
> with a Flight Recorder. You have to fly further to get a decent photo and
> the cockpit workload is significantly higher. Yet we award the same badge
> for both performances - thus some "unfairness" already exists in the code.

Positions are positions. Pressure altitudes are not heights or elevations.

>> Tying the COTS GPS rules to the use of GPS altitude would almost
>> certainly result in failure to pass the proposal. Requiring use of a
>> pressure altitude recording device (i.e. barograph) increases the
>> probability that a majority of the IGC delegates will vote in favor of
>> the proposal. That's politics for you...
>
> This political argument sounds far more plausible than any technical one.
> I would like to see a list of IGC delegates (identified by country) who
> are apposed to the use of GPS altitude to measure height gain. Then we
> could explain to them that their attitude is quietly killing our sport...

http://www.fai.org/directory/delegates.asp?id=6

The fact that you don't agree with the technical arguments doesn't
necessarily mean that they're wrong.

> To put it another way, if we accept COTS GPS together with COTS altitude,
> then overnight there would be 10000 Flarm equipped gliders which would
> each have their own dedicated Flight Recorder at no additional cost at
> all... Now that would be a powerful boost for our sport.

Flarm units have pressure sensors, there will be news fairly soon.

Marc

[[email protected]]

Marc wrote: Positions are positions. * Pressure altitudes are not
heights or elevations.

And yet the IGC calls them height gains for badges and absolute
altitude for records?

Bob (5 more weeks till flying season!)

[Ian Strachan]

> And what is so complicated in adding GPS altitiude as an IGC
> recognized measurement ? Especially since GPS lat,lon is a
> recognized. *I am serious, please tell me.
>
> Todd Smith
> 3S- Hide quoted text -

I am afraid that GPS altitude as recorded in IGC flight data files,
has been shown to be unreliable for accurate measurement purposes,
compared to traditional pressure altitude calibrated to the ICAO ISA.

In the Sporting Code, GPS altitude has always been OK for evidence of
flight continuity, but not where accurate figures are required such as
for gain-of-height or comparison with airspace bases. Some more
detail follows.

Pressure altitude is extremely reliable in IGC files and has a
negligible anomaly rate. In comparison, a significant proportion of
IGC files have GPS altitude anomalies, some small but some large. One
example is where high points are high and low points are low (compared
to pressure altitude), making gains-of-height different. If you look
closely at IGC file data, there are often differences between pressure
and GPS altitude that cannot be explained by the known differences
between the two due to atmospheric pressure changes and the different
scales. GPS altitude is vertical distance above the Geodetic Datum
that is selected (WGS84 for most purposes) whereas pressure altitude
used in aviation worldwide uses the ICAO International Standard
Atmosphere. In addition there are quite a few examples of major GPS
altitude anomalies in IGC files, involving differences from pressure
altitude not just of tens or hundreds of feet, but occasionally
thousands.

Another factor is that, even in ideal conditions, due to the geometry
of SatNav position lines making up a fix, altitude accuracy will
always be poorer than Lat/Long accuracy by a factor of about two.

A report on this was made to IGC in the year after the Selective
Availability accuracy degradation was removed on 1 May 2000. This
analysed many IGC files and came to the conclusion above. It was
posted on the IGC web site and may still be accessible if you look.
Many thousands of IGC files have been analysed since then and the
conclusion is still the same, anomalies in GPS altitude in IGC files
continue to occur. I say "in IGC files" because that is where the
data is from, and more expensive GPS receivers with more sophisticated
processing probably would not show these anomalies.

Fortunately, lat/long accuracy is not affected, the anomalies are
confined to GPS altitude. You might think that GPS receivers would
process one 3D position and then extract Lat/Long and altitude from
the same process. However, this appears not to be the way it is done
in the low-cost receivers used in IGC-approved recorders. Lat/Long is
processed separately from altitude and perhaps the manufacturer uses
more sophisticated processing for Lat/Long because that is what the
majority of customers want.

There is more, but the above summarises the reasons why IGC has, so
far, not added GPS altitude to the Sporting Code where accurate
measurements are required.

Ian Strachan
Lasham Gliding Centre, UK
Chairman IGC GNSS Flight Recorder Approval Committee (GFAC)

[Papa3]

On Feb 23, 6:28*am, Ian Strachan > wrote:

> Many thousands of IGC files have been analysed since then and the
> conclusion is still the same, anomalies in GPS altitude in IGC files
> continue to occur. *I say "in IGC files" because that is where the
> data is from, and more expensive GPS receivers with more sophisticated
> processing probably would not show these anomalies.
>
> >
> Ian Strachan
> Lasham Gliding Centre, UK
> Chairman IGC GNSS Flight Recorder Approval Committee (GFAC)

Ian,

I'd be curious to see the results of the detailed analysis of IGC
files. Is there a place on the IGC site where we could see the data?
I'm not looking for the annecdotal sort (i.e. see this file here) but
the volumetric sort (i.e. based on an automated review of 10,000
files). I had started on this a year back but stopped when I was
told that the IGC was already doing this.

In my experience in writing the specs for running a large batch
analysis program on this topic, what happens is that INDIVIDUAL fixes
or SMALL GROUPS of fixes do display anomalous results. I think most
people recongnize this possibility. However, they can easily be ruled
out by post-flight analysis programs by predefined parameters (for
example, a 10,000 fpm climb rate over a rolling 4 or 6 fix
average).

I think the bigger question that still needs to be answered is "to
what level of precision" do we need all of this to work.
Considering the inherent issues in measuring pressure altitude during
the fluid conditions of a post-frontal day (for example), it feels as
if we are holding GPS to a higher standard.

Thanks in advance,

Erik Mann

[Chip Bearden]

Ian,

I and many others appreciate your long, dedicated service and
willingness to interact on this forum. Please take these questions as
genuine requests to understand better the issues involved, not as an
attempt to undermine your position:

> I am afraid that GPS altitude as recorded in IGC flight data files,
> has been shown to be unreliable for accurate measurement purposes,
> compared to traditional pressure altitude calibrated to the ICAO ISA.

How are "reliable" and "unreliable" defined here? Given that there is
no independent verification of either method of determining altitude
(pressure and GPS)--at least in IGC files--I assume you use some
measure of the number and severity anomalies. Could you elaborate?

> Pressure altitude is extremely reliable in IGC files and has a
> negligible anomaly rate. *In comparison, a significant proportion of
> IGC files have GPS altitude anomalies, some small but some large. *

Could you give be more specific? Does reliability involve any
comparison of the two methods to cross check each other? That is, if
there's a sudden change in pressure altitude, is that presumed to be
in error solely because of the severity of the change or also because
the GPS altitude didn't change in a corresponding manner (and vice
versa)?

> In addition there are quite a few examples of major GPS
> altitude anomalies in IGC files, involving differences from pressure
> altitude not just of tens or hundreds of feet, but occasionally
> thousands.

Same question: is an anomaloy defined as a discontinuity in the trace
of a GPS or pressure altitude record, or a difference between the two
traces, or both? The above statement seems to indicate that the
difference between the two is taken into account. If so, are you
comfortable with judging the accuracy of one method by assuming the
other is correct?

> Another factor is that, even in ideal conditions, due to the geometry
> of SatNav position lines making up a fix, altitude accuracy will
> always be poorer than Lat/Long accuracy by a factor of about two.

What does this translate to in feet or meters, or in percentage terms?
And how does that compare with known accuracy of pressure altitudes?

> A report on this was made to IGC in the year after the Selective
> Availability accuracy degradation was removed on 1 May 2000. *This
> analysed many IGC files and came to the conclusion above. *It was
> posted on the IGC web site and may still be accessible if you look.
> Many thousands of IGC files have been analysed since then and the
> conclusion is still the same, anomalies in GPS altitude in IGC files
> continue to occur. *I say "in IGC files" because that is where the
> data is from, and more expensive GPS receivers with more sophisticated
> processing probably would not show these anomalies.

Do these "more expensive GPS receivers" refer to some or all current
COTS receivers, or to something else?

If comparisons of pressure and GPS altitudes are made to determine
anomalies, are they based solely on the records in approved flight
recorders or also on comparisons of traces made with other GPS
receivers. For example, I carry a Garmin GPSMAP 76 as a backup and
have downloaded and compared its trace with that of my Cambridge Model
20 for a number of flights. There are differences, as you say, but as
a layman I have no way of knowing which is closer to being correct.
And I have not compared the GPS altitude from the Cambridge to the GPS
altitude from the Garmin. Do the studies to which you refer do this?

> Fortunately, lat/long accuracy is not affected, the anomalies are
> confined to GPS altitude. *You might think that GPS receivers would
> process one 3D position and then extract Lat/Long and altitude from
> the same process. *However, this appears not to be the way it is done
> in the low-cost receivers used in IGC-approved recorders. *Lat/Long is
> processed separately from altitude and perhaps the manufacturer uses
> more sophisticated processing for Lat/Long because that is what the
> majority of customers want.

This is an interesting speculation. How likely is it that if the
flight recorder manufacturers wished to reduce anomalies in their GPS
altitude records, they could do so? And (this is purely speculative on
my part) would you agree there has been a disincentive for them to do
so since the more accurate that GPS altitude is proven to be, the more
likely that they might lose their exclusivity in the gliding
market?

> There is more, but the above summarises the reasons why IGC has, so
> far, not added GPS altitude to the Sporting Code where accurate
> measurements are required.

I know that years ago there was a strong, justifiable sense of
appreciation for the work that Dave Ellis and Cambridge did to make
flight recorders possible and affordable for many pilots. Without
implying that GFAC or the IGC felt any moral obligation in the past to
"reward" this dedication by excluding other types of flight recorders
or verification methods, do you believe the flight recorder market is
well enough established now that new entrants, whether they be COTS
manufacturers or soaring equipment builders, are viewed without any
consideration for the early days of flight recorders or the difficulty
of making a profit in the relatively small world of gliding? To be
more provocative, is there any concern over the fact that opening up
the market to COTS equipment now would almost certainly harm flight
recorder manufacturers?

Chip Bearden
ASW 24 "JB"
USA

[Bill Daniels]

First, I wish to complement the IGC for it's work on GPS flight loggers.
They have made a huge and favorable impact on soaring performance and cross
country flying. The fact that the availible certified units aren't cheap
enough to satisfy all is just an artifact and not at all the intention of
the IGC. I'm sure everyone in the IGC hopes time will bring cheaper units.

For those pilot wishing to attempt a badge flight, just ask to borrow a
logger from a fellow pilot. My Volkslogger is available for the asking - as
long as I know you.

Now, some rambling thoughts.

Both pressure altitude and GPS altitude sensors suffer a "signal to noise"
ratio but of a different character.

In the case of pressure sensors, the main source of "noise" is the synoptic
distribution of highs and lows on the weather map. This noise signal
changes slowly over time scales of hours and distances of hundreds of miles.
There are errors due to differences in the temperature of the atmospheric
collumn and the Standard Atmosphere which change slowly on a daily cycle.
There may also be a shorter time scale noise source related to the static
source or cockpit pressure although this is small compared to synoptic
pressure changes.

A GPS receiver, by nature of being a radio, suffers noise of a different
type. 'Static' is short term noise on the scale of milliseconds. There is
also some noise from the slowly changing geometry of the Navstar satelites
but this is predictable, thus not really 'noise'. There's also the issue of
each system using a different sea level reference or "datum"

Both GPS altitude and pressure altitude are both "right" and "wrong" for
different reasons.

Sometimes, a clever engineer can fuse data from two different sources in a
way that uses the best of each and cancels out the worst. This is seen in
fusing data using a Kalman Filter from a GPS receiver and an Inertial
Measurement Unit. GPS, is a 'position finding system' and the IMU is a
'position keeping system'. GPS keeps the IMU honest and the IMU smooths out
the GPS signal. The result is basically a huge "signal to noise"
improvement.

Simularly, fusing pressure data with GPS altitude data could work the same
way. For example, a millisecond scale spike in GPS altitude, not confirmed
by presure data could be ignored with impunity. A slow drift of the
pressure signal from the smoothed GPS signal is almost certainly a synoptic
pressure change and can be canceled by the long term stability of the GPS
signal making the pressure signal more useful in detecting airspace
incursions. (Think automatic Kollsman settings.)

The differences between sea level references and temperatue differences from
the Standard Atmosphere can be subrtacted out producing an altitude signal
referenced to whatever datum you choose.

Of course, all this ignores the question of just what it is you want to
measure. If it is deemed desirable to have an altitude logging system for
future flights that is directly comparable to past flights that used a
barograph, then including GPS data may not be desirable.

Does any of this have something to do with reducing the cost of loggers?
Maybe. If two low cost sensors fused together can produce superior data to
one high cost sensor, the result might be a cheaper, more accurate logger.

Bill Daniels

[Papa3]

On Feb 23, 1:08*pm, "Bill Daniels" <bildan@comcast-dot-net> wrote:

>
>
> Simularly, fusing pressure data with GPS altitude data could work the same
> way. *For example, a millisecond scale spike in GPS altitude, not confirmed
> by presure data could be ignored with impunity. *A slow drift of the
> pressure signal from the smoothed GPS signal is almost certainly a synoptic
> pressure change and can be canceled by the long term stability of the GPS
> signal making the pressure signal more useful in detecting airspace
> incursions. *(Think automatic Kollsman settings.)

>
> Bill Daniels

Which, interestingly, is exactly what the $200 Garmins with Pressure
Sensor do!

P3

[Chip Bearden]

On Feb 23, 5:52*pm, Papa3 > wrote:
> On Feb 23, 1:08*pm, "Bill Daniels" <bildan@comcast-dot-net> wrote:
>
>
>
> > Simularly, fusing pressure data with GPS altitude data could work the same
> > way. *For example, a millisecond scale spike in GPS altitude, not confirmed
> > by presure data could be ignored with impunity. *A slow drift of the
> > pressure signal from the smoothed GPS signal is almost certainly a synoptic
> > pressure change and can be canceled by the long term stability of the GPS
> > signal making the pressure signal more useful in detecting airspace
> > incursions. *(Think automatic Kollsman settings.)
>
> > Bill Daniels
>
> Which, interestingly, is exactly what the $200 Garmins with Pressure
> Sensor do!
>
> P3

So, in effect, IGC/GFAC are holding back progress on better altitude
measurement--at lower cost--by refusing to allow [certain] COTS
receivers? :) Come on, folks, this is the 21st century. Technology
should be welcomed, not feared!

Chip Bearden
ASW 24 "JB"
USA

[Marc Ramsey[_2_]]

Papa3 wrote:
> On Feb 23, 1:08 pm, "Bill Daniels" <bildan@comcast-dot-net> wrote:
>
>>
>> Simularly, fusing pressure data with GPS altitude data could work the same
>> way. For example, a millisecond scale spike in GPS altitude, not confirmed
>> by presure data could be ignored with impunity. A slow drift of the
>> pressure signal from the smoothed GPS signal is almost certainly a synoptic
>> pressure change and can be canceled by the long term stability of the GPS
>> signal making the pressure signal more useful in detecting airspace
>> incursions. (Think automatic Kollsman settings.)
>
>> Bill Daniels
>
> Which, interestingly, is exactly what the $200 Garmins with Pressure
> Sensor do!

Garmins do not have calibrated pressure sensors, in the "auto
calibration" mode, you get smoothed GPS (geometric) altitude, not
calibrated pressure altitude. Without additional information from
outside weather sources, it can't be used for detecting airspace
incursions. An altimeter setting is a temperature corrected "sea level"
pressure setting for a specific reporting station. There will still be
discrepancies between pressure and geometric altitude at anything other
than the elevation of the station, as the average temperature of the air
column between will almost never match that modeled by the International
Standard Atmosphere. This discrepancy can amount to over 1000 feet at
10000 feet above the station on a hot summer day...

Marc

[Papa3]

On Feb 23, 7:10*pm, Marc Ramsey > wrote:
> Papa3 wrote:
> > On Feb 23, 1:08 pm, "Bill Daniels" <bildan@comcast-dot-net> wrote:
>
> >> Simularly, fusing pressure data with GPS altitude data could work the same
> >> way. *For example, a millisecond scale spike in GPS altitude, not confirmed
> >> by presure data could be ignored with impunity. *A slow drift of the
> >> pressure signal from the smoothed GPS signal is almost certainly a synoptic
> >> pressure change and can be canceled by the long term stability of the GPS
> >> signal making the pressure signal more useful in detecting airspace
> >> incursions. *(Think automatic Kollsman settings.)
>
> >> Bill Daniels
>
> > Which, interestingly, is exactly what the $200 Garmins with Pressure
> > Sensor do!
>
> Garmins do not have calibrated pressure sensors, in the "auto
> calibration" mode, you get smoothed GPS (geometric) altitude, not
> calibrated pressure altitude. *Without additional information from
> outside weather sources, it can't be used for detecting airspace
> incursions. *An altimeter setting is a temperature corrected "sea level"
> pressure setting for a specific reporting station. *There will still be
> discrepancies between pressure and geometric altitude at anything other
> than the elevation of the station, as the average temperature of the air
> column between will almost never match that modeled by the International
> Standard Atmosphere. *This discrepancy can amount to over 1000 feet at
> 10000 feet above the station on a hot summer day...
>
> Marc- Hide quoted text -
>
> - Show quoted text -

Who said anything about airspace incursions? What we are talking
about is filtering "noise" from spurious GPS signals. It presents an
interesting possibility for providing real-time (as oposed to post-
flight) noise cancelling.

I should have snipped the second part of Bill's post, as that again
gets us back to the GPS vs. Pressure altitude debate.

P3

[Marc Ramsey[_2_]]

Papa3 wrote:
> On Feb 23, 7:10 pm, Marc Ramsey > wrote:
>> Papa3 wrote:
>>> On Feb 23, 1:08 pm, "Bill Daniels" <bildan@comcast-dot-net> wrote:
>>>> Simularly, fusing pressure data with GPS altitude data could work the same
>>>> way. For example, a millisecond scale spike in GPS altitude, not confirmed
>>>> by presure data could be ignored with impunity. A slow drift of the
>>>> pressure signal from the smoothed GPS signal is almost certainly a synoptic
>>>> pressure change and can be canceled by the long term stability of the GPS
>>>> signal making the pressure signal more useful in detecting airspace
>>>> incursions. (Think automatic Kollsman settings.)
>>>> Bill Daniels
>>> Which, interestingly, is exactly what the $200 Garmins with Pressure
>>> Sensor do!
>> Garmins do not have calibrated pressure sensors, in the "auto
>> calibration" mode, you get smoothed GPS (geometric) altitude, not
>> calibrated pressure altitude. Without additional information from
>> outside weather sources, it can't be used for detecting airspace
>> incursions. An altimeter setting is a temperature corrected "sea level"
>> pressure setting for a specific reporting station. There will still be
>> discrepancies between pressure and geometric altitude at anything other
>> than the elevation of the station, as the average temperature of the air
>> column between will almost never match that modeled by the International
>> Standard Atmosphere. This discrepancy can amount to over 1000 feet at
>> 10000 feet above the station on a hot summer day...
>>
>> Marc- Hide quoted text -
>>
>> - Show quoted text -
>
> Who said anything about airspace incursions? What we are talking
> about is filtering "noise" from spurious GPS signals. It presents an
> interesting possibility for providing real-time (as oposed to post-
> flight) noise cancelling.

Bill mentioned airspace incursions in the quote that you included. The
described filtering technique does a decent job of smoothing GPS
altitude, but not at all helpful if what you really want is pressure
altitude.

> I should have snipped the second part of Bill's post, as that again
> gets us back to the GPS vs. Pressure altitude debate.

That's the thing, though, it doesn't much matter whether GPS altitude
has the noise filtered out or not, what the IGC currently wants is
pressure altitude.

Marc

[Dan[_4_]]

First, let me echo what Bill Daniels said - the GFAC are doing great
work on igc recorders, all of us appreciate not having to use cameras
at the turnpoint. Second, like him, I loan my Volkslogger to anyone
who wants to use it when I'm not in the search for my third diamond.

My problem with COTS gps systems is more practical. The Dilution of
Precision (DOP) in the z-axis is latitude-dependant; this is due to
the orbits of the satellites (see, Electronic Navigation Systems,
Bjorie Forsell - simply, DOP is how "good" the gps 3-D fix is). For
glider pilots in northern climes, this is a problem. Having to obtain
a more-expensive system just because you live in a winter wonderland
seems unfair. Straight precision (geometric DOP) of the GPS system is
also variable (and that's if you don't fly in the US, where the Dept
of Defense is practicing gps denial many weekdays).

First, let's get some toys to play with; a good, free gps analyzer
from Trimble is their planning software, at http://www.trimble.com/planningsoftware_ts.asp.
Download it. Start it. You have to put in an almanac, from Trimble
gps data resources, further down the page (download in ssf format,
import it to the planning software using the 'import' feature). Now
you're set. Let's assume I'm doing a 5 hr today at Alert, Nunavut,
Canada, 8228N 06230W (a Canadian Forces Station, "we supply Santa").
Input today's date - Feb 24, 2008, 24 period. Input the appropriate
coordinates in 'station' pulldown.
Take a look at the pull-down chart for vertical DOP (wiki has a good
discussion of DOP that's not mathematically intense). Note that the Z-
precision of the gps signals is not useable around 0745 and, to a
lesser extent, around 1130. So, a altitude badge at this place and
time would not be possible. Having a system that predictably doesn't
work sometimes for z-precision (altitude) as our method of doing
altitude claims seems optimistic (other words also occur). Pull-down
the station to Munich, and see that at various times today, it's also
not great. Try Omarama, NZ, approx 4430S, 17000E - look at 1800
today - not useable. It would be interesting to look at olc traces
today from around there to see if there was an effect...

Now, put in YOUR lat/long and take a look at the V-DOP for a 24 hr
period at your home station; you may be lucky, and see no problems;
extend the period, and have another look. GPS geometry is pretty
tricky. As an Official Observer, I use this software to take a look
at igc files when the system has x-y problems - and most times, the x
or y-DOP sucks at the time. Note, US Coast Guard GPS status and NANUs
(Notice to Navstar Users) are also available from the Trimble gps data
sources page; it should be checked if you intend to use GPS on a
flight (good info for Contest Directors). Good one to bookmark.

Use of COTS for horizontal fixing is a great idea, though as an OO I'm
not wild about having to learn a bunch of new systems. Using gps for
altitude is a big mistake, and the GFAC is to commended for not going
that way. Those who say that COTS gps seems to be the way to go are
correct; it SEEMS to be. Take a closer look at the details
(apparently, the devil is in them) and it's not so clear anymore. The
US military does move the satellites to improve precision at times
(Gulf Wars), and the accuracy back in North America is degraded
somewhat, and Selective Availability is currently set to zero, and
could come back in certain circumstances.

I have experience in testing electronic navigation systems (incl GPS)
on a large fixed wing aircraft as an operational test and evaluation
project officer (if you have one system, you know where you are; with
three, you're never quite sure...), have a graduate degree including
work in this area, some software background, and a number of years
flying in the school of hard knocks. I've been playing with
electronic data recorders since 1997.

I hope everyone has fun with the software; I have my flame-proof suit
on; what do you think?

Dan
Yes, it's cold, and in lieu of flying, I use GPS analysis software...
<sigh>

[Martin Gregorie[_1_]]

Dan wrote:
> My problem with COTS gps systems is more practical. The Dilution of
> Precision (DOP) in the z-axis is latitude-dependant;
<snippage>

Thanks for the explanation. Its cleared up a few things I'd wondered about.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[PCool]

"Marc Ramsey" > ha scritto nel messaggio
et...
> pressure setting for a specific reporting station. There will still be
> discrepancies between pressure and geometric altitude at anything other
> than the elevation of the station, as the average temperature of the air
> column between will almost never match that modeled by the International
> Standard Atmosphere. This discrepancy can amount to over 1000 feet at
> 10000 feet above the station on a hot summer day...


Marc are you saying that these devices such as Garmin's S serie (baro
sensors, temperature sensor for GPS altitude corrections) can be 1000 to
10000 feet wrong?

Thanks for answering
Paul

[PCool]

I just found the patent by Garmin dated 2001 and registered in 2004 where
the altitude calculation using bot a pressure sensor and a GPS is explained.
They talk about ICAO ISA reference, but maybe Ian will be helpful to explain
what's in there.
This is the link, I found it very interesting
http://www.patentstorm.us/patents/6735542-description.html

Anyone can comment on this , in respect to what the IGC requires for
altitude readings?

Paul


"PCool" > ha scritto nel messaggio
...
>
> "Marc Ramsey" > ha scritto nel messaggio
> et...
>> pressure setting for a specific reporting station. There will still be
>> discrepancies between pressure and geometric altitude at anything other
>> than the elevation of the station, as the average temperature of the air
>> column between will almost never match that modeled by the International
>> Standard Atmosphere. This discrepancy can amount to over 1000 feet at
>> 10000 feet above the station on a hot summer day...
>
>
> Marc are you saying that these devices such as Garmin's S serie (baro
> sensors, temperature sensor for GPS altitude corrections) can be 1000 to
> 10000 feet wrong?
>
> Thanks for answering
> Paul
>

[Marc Ramsey[_2_]]

PCool wrote:

> Marc are you saying that these devices such as Garmin's S serie (baro
> sensors, temperature sensor for GPS altitude corrections) can be 1000 to
> 10000 feet wrong?

This was in the context of "fusing" the GPS altitude with the pressure
sensor, which results in smoothed GPS altitude, rather than pressure
altitude. If you don't manually calibrate against a known elevation or
pressure, a Garmin "S" unit will continuously auto-calibrate in
precisely this fashion. When you look at GPS altitude relative to
pressure altitude, pressure altitude will show expected errors
proportional to altitude, which can range upwards of 1000 feet during
summer months at 10000 feet AGL.

Pressure altimeters, like the altimeter sitting in your instrument panel
and the pressure sensors in flight recorders, do not measure altitude,
they measure pressure. The conversion between pressure and altitude
uses an atmosphere model called the International Standard Atmosphere
(ISA) that specifies a sea level pressure of 101.3 kPa (29.92" Hg),
temperature of 15C, and divides the atmosphere into a series of layers,
each with a specific linear temperature lapse rate. The problem is, the
atmosphere never exactly matches the model, so there is always some
amount of error in the conversion.

In particular, if the average temperature of the column of air between a
reporting station and an aircraft overhead doesn't match the model,
the pressure gradient also won't match the model, so the altitude
indicated by a correctly set altimeter will not match the actual
elevation above nominal sea level.

The easiest way to see this is in an IGC file from an approved flight
recorder. During summer months, note the relative difference between
the pressure and GPS altitude at the lower and higher altitudes. As
altitude increases, GPS altitude will increase relative to pressure
altitude, as pressure altitude is reading too low at higher altitudes.
Here in the western US, we can see this clearly near mountain peaks, as
a correctly set altimeter will be reading as much as 1000 feet too low,
whereas GPS altitude matches the known elevations of the peaks.

If a Garmin "S" unit could be set to a fixed calibration equivalent to a
pressure of 29.92 in. mercury, and the temperature compensation and
stability was adequate, it would provide readings equivalent to the
pressure sensor in an approved flight recorder. With any sort of
automatic or continuous recalibration enabled, this is no longer true.

Marc

[Chip Bearden]

On Feb 24, 7:07*pm, Marc Ramsey > wrote:

> The easiest way to see this is in an IGC file from an approved flight
> recorder. *During summer months, note the relative difference between
> the pressure and GPS altitude at the lower and higher altitudes. *As
> altitude increases, GPS altitude will increase relative to pressure
> altitude, as pressure altitude is reading too low at higher altitudes.
> Here in the western US, we can see this clearly near mountain peaks, as
> a correctly set altimeter will be reading as much as 1000 feet too low,
> whereas GPS altitude matches the known elevations of the peaks.

OK, I'm a layman, late middle age, and little slow. What am I missing?
The pressure altitude (per the altimeter, at least) is less accurate
than the GPS altitude? By up to 1000 feet at Western USA soaring
altitudes? In the old days, we used a start gate that evaluated
optically how high we were above the ground. Assuming no one tripped
over the guy wires, that actual altitude stayed the same during a
contest. Now we're evaluated using a pressure-altitude-recording
device that may or may not reflect how high we really are?

Do the experts maintain that GPS altitude is bad because (a) it
DOESN'T have the errors inherent in pressure altitude or (b) because
its precision isn't good enough? It seems like I've seen both
positions on this forum.

Chip Bearden
ASW 24 "JB"
USA

[Marc Ramsey[_2_]]

Chip Bearden wrote:
> On Feb 24, 7:07 pm, Marc Ramsey > wrote:
>
>> The easiest way to see this is in an IGC file from an approved flight
>> recorder. During summer months, note the relative difference between
>> the pressure and GPS altitude at the lower and higher altitudes. As
>> altitude increases, GPS altitude will increase relative to pressure
>> altitude, as pressure altitude is reading too low at higher altitudes.
>> Here in the western US, we can see this clearly near mountain peaks, as
>> a correctly set altimeter will be reading as much as 1000 feet too low,
>> whereas GPS altitude matches the known elevations of the peaks.
>
> OK, I'm a layman, late middle age, and little slow. What am I missing?
> The pressure altitude (per the altimeter, at least) is less accurate
> than the GPS altitude? By up to 1000 feet at Western USA soaring
> altitudes? In the old days, we used a start gate that evaluated
> optically how high we were above the ground. Assuming no one tripped
> over the guy wires, that actual altitude stayed the same during a
> contest. Now we're evaluated using a pressure-altitude-recording
> device that may or may not reflect how high we really are?

Once again, pressure altitude and GPS altitude measure two different
things using the same units. Because we like to fly when there is a
non-standard temperature lapse rate, there is almost always noticeable
pressure altitude error above a few thousand feet AGL. If an optical
start gate is showing the actual heights, most gliders will appear to be
starting high, since the altimeters are reading low, and the validity of
the start is determined from the recorded pressure altitude. Those
pilots who are recording only GPS altitude (GPS handhelds, etc.) need to
be careful, as they start will be scored based on actual height, which
means they have to start lower. They need to be watching the GPS
display, rather then the altimeter, when they are flirting with the top
of the start cylinder.

> Do the experts maintain that GPS altitude is bad because (a) it
> DOESN'T have the errors inherent in pressure altitude or (b) because
> its precision isn't good enough? It seems like I've seen both
> positions on this forum.

As you know, experts generally maintain whatever favors their position.
Look at it this way, GPS altitude is more accurate at measuring actual
height, pressure altitude is more accurate at measuring, well, pressure
altitude. Since one function of the flight recorder is to detect and
penalize airspace incursions, pressure altitude will continue to be a
consideration, no matter what else happens. Some of the other air
sports, like ballooning, have already switched over to using actual
height, they use sounding data and software to convert to/from pressure
altitude as needed.

Marc

[Marc Ramsey[_2_]]

Chip Bearden wrote:
> OK, I'm a layman, late middle age, and little slow. What am I missing?
> The pressure altitude (per the altimeter, at least) is less accurate
> than the GPS altitude? By up to 1000 feet at Western USA soaring
> altitudes? In the old days, we used a start gate that evaluated
> optically how high we were above the ground. Assuming no one tripped
> over the guy wires, that actual altitude stayed the same during a
> contest. Now we're evaluated using a pressure-altitude-recording
> device that may or may not reflect how high we really are?

As an aside, while I flew a few contests using optical start gates, I
can't remember how one used to avoid bad starts. Did we dive through
with enough of a buffer beneath the stated maximum start altitude to
allow for the pressure altimetry error, or did we generally start lower
(so the wing numbers could be read through binoculars), thus keeping
error pretty small?

Marc

[PCool]

Thanks Marc,

is it correct to say that the Pressure Altitude is an altitude calculated
starting from a pressure value, following a sort-of a rule as for ICAO-ISA ?
I guess official IGC loggers read the exact pressure as garmins and suunto
watches (!) and then they apply some calculations and name this result as
"altitude".
Do they do this without looking at what the GPS say?? Not even for an hint?

What is the formula used by all IGC loggers for doing this, then?

It's beyond my comprehension why if we are talking about pressure which is
always measured in the same way (right?) then this value has different
meanings and cannot be simply converted like with QNE-QNH-QFE.
ICAO-ISA is sort of a more complicated QNE, right? (question!)

On garmins you have a pressure sensor just like on a Colibrì, then this
sensor is used to compensate the gps and vice-versa, according to the patent
they have registered. By the way Marc could you understand anything useful
out of it?

After 4 years there are again the same questions on this matter so I guess
it's not very clear to everybody (me too).

thanks!
Paolo



"Marc Ramsey" > ha scritto nel messaggio
et...
>
> Once again, pressure altitude and GPS altitude measure two different
> things using the same units. Because we like to fly when there is a
> non-standard temperature lapse rate, there is almost always noticeable
> pressure altitude error above a few thousand feet AGL. If an optical
> start gate is showing the actual heights, most gliders will appear to be
> starting high, since the altimeters are reading low, and the validity of
> the start is determined from the recorded pressure altitude. Those pilots
> who are recording only GPS altitude (GPS handhelds, etc.) need to be
> careful, as they start will be scored based on actual height, which means
> they have to start lower. They need to be watching the GPS display,
> rather then the altimeter, when they are flirting with the top of the
> start cylinder.
>
>> Do the experts maintain that GPS altitude is bad because (a) it
>> DOESN'T have the errors inherent in pressure altitude or (b) because
>> its precision isn't good enough? It seems like I've seen both
>> positions on this forum.
>
> As you know, experts generally maintain whatever favors their position.
> Look at it this way, GPS altitude is more accurate at measuring actual
> height, pressure altitude is more accurate at measuring, well, pressure
> altitude. Since one function of the flight recorder is to detect and
> penalize airspace incursions, pressure altitude will continue to be a
> consideration, no matter what else happens. Some of the other air sports,
> like ballooning, have already switched over to using actual height, they
> use sounding data and software to convert to/from pressure altitude as
> needed.
>
> Marc

[Tim Taylor]

On Feb 24, 11:45 pm, Marc Ramsey > wrote:
> Chip Bearden wrote:
> > OK, I'm a layman, late middle age, and little slow. What am I missing?
> > The pressure altitude (per the altimeter, at least) is less accurate
> > than the GPS altitude? By up to 1000 feet at Western USA soaring
> > altitudes? In the old days, we used a start gate that evaluated
> > optically how high we were above the ground. Assuming no one tripped
> > over the guy wires, that actual altitude stayed the same during a
> > contest. Now we're evaluated using a pressure-altitude-recording
> > device that may or may not reflect how high we really are?
>
> As an aside, while I flew a few contests using optical start gates, I
> can't remember how one used to avoid bad starts. Did we dive through
> with enough of a buffer beneath the stated maximum start altitude to
> allow for the pressure altimetry error, or did we generally start lower
> (so the wing numbers could be read through binoculars), thus keeping
> error pretty small?
>
> Marc

Marc,

It was like Tennis. You went for two serves, the first was redline
and right at altitude. If Charlie said good start you had scored an
ace and were on your way. If you got a fault (bad start) you went
back and added a hundred or two hundred feet as a safety margin.

Ah, the fun of multiple ships diving at a gate at redline at the same
time and aggressive prestart gaggles to get that extra 1000 feet so
you could dive.

Thanks BB for the new rules!

Tim

[Marc Ramsey[_2_]]

PCool wrote:
> Thanks Marc,
>
> is it correct to say that the Pressure Altitude is an altitude calculated
> starting from a pressure value, following a sort-of a rule as for ICAO-ISA ?
> I guess official IGC loggers read the exact pressure as garmins and suunto
> watches (!) and then they apply some calculations and name this result as
> "altitude".

Yes

> Do they do this without looking at what the GPS say?? Not even for an hint?

Yes, the calibration is fixed at the time the recorder leaves the
manufacturer, and subsequent visits to the calibration lab simply
provide you with the data to manually correct the original calibration.

> What is the formula used by all IGC loggers for doing this, then?

The details can be found here, in the section Standard Atmosphere and
Altimetry:

http://williams.best.vwh.net/avform.htm#Altimetry


> It's beyond my comprehension why if we are talking about pressure which is
> always measured in the same way (right?) then this value has different
> meanings and cannot be simply converted like with QNE-QNH-QFE.
> ICAO-ISA is sort of a more complicated QNE, right? (question!)

The ISA model assumes a standard lapse rate (0.0065°C/m) below the
tropopause (11.0 km), the real atmosphere is more complicated, which is
what causes the error. Altimeters are mechanical computers which do a
simple ISA to indicated altitude conversion, flight recorders do it in
software (but use the fixed 1013.2 hPa altimeter setting), in the end
they all have the same errors relative to actual height on days when the
lapse rate differs from the standard (which is every day). Calculating
QNH requires an inverted application of the ISA conversion, the weather
guys do it in the privacy of their offices.

> On garmins you have a pressure sensor just like on a Colibrì, then this
> sensor is used to compensate the gps and vice-versa, according to the patent
> they have registered. By the way Marc could you understand anything useful
> out of it?

Yes, they are describing in very mechanical terms (which is how you get
a patent on a software process) how to use GPS altitude to continuously
recalibrate the pressure sensor, such that you obtain actual height (but
not ISA/QNH indicated altitude) without the short term noise normally
present in GPS altitude. This is what was discussed earlier in the thread.

> After 4 years there are again the same questions on this matter so I guess
> it's not very clear to everybody (me too).

I have to think about it myself every time it comes up, I can never
remember if altimeters read high or low on hot days. And, I still can't
keep my Q codes straight, which I no doubt demonstrated above...

Marc

[PCool]

Thank you Mark, now it is all very clear to me, finally.

I wish to do a summary of what I have understood, very simplified.

What is Pressure Altitude for IGC standards
It is the altitude calculated with an ICAO-ISA formula . You need a baro
which has been calibrated at the factory, because the calibration is fixed
at the time the recorder leaves the manufacturer (just like mechanical
baro). The calibration is an important issue (exactly just like for the old
good mechanical barographs). Once calibrated, you read a pressure value.
You pass this value to a formula and get the ICAO-ISA altitude. In
practice, QNE and ICAO-ISA may differ by some tens of meters, once
calculated on the same value!
You can revert the formula: starting from an ICAO-ISA altitude you can get
the pressure.

What is Altitude for a Garmin and/or a GPS COTS
The altitude measured by a GPS could be the real altitude over ground, but
intrinsecally may contain geometric errors. Everyone agree on the fact that
the GPS Altitude is not accurate.
Some GPS like Garmin's use baro sensor to correct the GPS altitude, and
vice-versa, in order to achieve maximum precision and obtain possibly the
Real Altitude, above mean sea level. When we say "correct altitude" normally
we refer to this.

Why COTS' Altitude is not good for IGC badges
The answer has nothing to do with precision. IGC requires to read ICAO
Pressure-Altitude, not the real altitude.
It is exactly the same altitude you may read on a paper from an old
barograph.
There could be little difference among the two, but in principle we are not
talking about the same thing.
Of course a COTS could easily output an ICAO-ISA altitude, it's just a
matter of using the formula and unselect any other corrections. The
manufacturer could thus implement this feature, it is much easier than
correcting and auto-calibrating GPS altitude.
BUT, but, the manufacturer should also provide a calibrated sensor at the
factory.

In other words: if three devices are standing at the same height, they
should all read the same pressure value, say 747 mb.
The garmin with sensor may say you are at 4750m , another COTS basing only
on GPS may read 4680m, while the IGC may declare 4820m.

Conclusion: without a pressure sensor no COTS can be used today as an
alternative to IGC altitude loggers.
And in any case, calibration is an issue.



-- Mark did I get it right?
Paolo







"Marc Ramsey" > ha scritto nel messaggio
et...
> PCool wrote:
>> Thanks Marc,
>>
>> is it correct to say that the Pressure Altitude is an altitude calculated
>> starting from a pressure value, following a sort-of a rule as for
>> ICAO-ISA ?
>> I guess official IGC loggers read the exact pressure as garmins and
>> suunto watches (!) and then they apply some calculations and name this
>> result as "altitude".
>
> Yes
>
>> Do they do this without looking at what the GPS say?? Not even for an
>> hint?
>
> Yes, the calibration is fixed at the time the recorder leaves the
> manufacturer, and subsequent visits to the calibration lab simply provide
> you with the data to manually correct the original calibration.
>
>> What is the formula used by all IGC loggers for doing this, then?
>
> The details can be found here, in the section Standard Atmosphere and
> Altimetry:
>
> http://williams.best.vwh.net/avform.htm#Altimetry
>
>
>> It's beyond my comprehension why if we are talking about pressure which
>> is always measured in the same way (right?) then this value has different
>> meanings and cannot be simply converted like with QNE-QNH-QFE.
>> ICAO-ISA is sort of a more complicated QNE, right? (question!)
>
> The ISA model assumes a standard lapse rate (0.0065°C/m) below the
> tropopause (11.0 km), the real atmosphere is more complicated, which is
> what causes the error. Altimeters are mechanical computers which do a
> simple ISA to indicated altitude conversion, flight recorders do it in
> software (but use the fixed 1013.2 hPa altimeter setting), in the end they
> all have the same errors relative to actual height on days when the lapse
> rate differs from the standard (which is every day). Calculating QNH
> requires an inverted application of the ISA conversion, the weather guys
> do it in the privacy of their offices.
>
>> On garmins you have a pressure sensor just like on a Colibrì, then this
>> sensor is used to compensate the gps and vice-versa, according to the
>> patent they have registered. By the way Marc could you understand
>> anything useful out of it?
>
> Yes, they are describing in very mechanical terms (which is how you get a
> patent on a software process) how to use GPS altitude to continuously
> recalibrate the pressure sensor, such that you obtain actual height (but
> not ISA/QNH indicated altitude) without the short term noise normally
> present in GPS altitude. This is what was discussed earlier in the
> thread.
>
>> After 4 years there are again the same questions on this matter so I
>> guess it's not very clear to everybody (me too).
>
> I have to think about it myself every time it comes up, I can never
> remember if altimeters read high or low on hot days. And, I still can't
> keep my Q codes straight, which I no doubt demonstrated above...
>
> Marc

[Chip Bearden]

On Feb 25, 12:53*pm, "PCool" > wrote:
> Everyone agree on the fact that
> the GPS Altitude is not accurate.

Actually, what I took away from this discussion is that the GPS
altitude is MORE accurate with regard to actual height above the
ground but not necessarily equal to pressure altitude in the real
world. So what I hear now is the Certified Flight Recorder crowd
saying we shouldn't use GPS altitude even if it's more accurate, for
the reason that it's not comparable with the way we've always
evaluated badge and record claims in the past. This seems precisely
the opposite argument used to justify GPS flight recorders in the
first place: i.e., that their 2D positional accuracy was better so we
simply *must* use it. :)

I agree airspace incursions are a different issue. But in the old
days, we could only measure incursions on the Y axis (i.e. altitude)
anyway. Would it be so bad if now we could only measure them on the X
and Z axes (i.e., lat/long)? At most contests where I've flown
recently, including US Nationals, that's been the case: i.e., we're
not allowed to fly over or under most airspace that is restricted to
gliders. Worst case, users of COTS receivers might have to self impose
that condition or leave, say, a 1,000 ft. buffer

I'm not trying to make trouble but I'm genuinely baffled as to what is
the problem. If GPS altitude is more accurate and COTS receivers are
no more vulnerable to a determined hacker than, say, my Cambridge
Model 20 (which I've had open several times), then why not allow them?
Saying that the casual pilot can easily borrow an expensive Certified
Flight Recorder from a more serious, more affluent club member on
occasion is sort of like prohibiting the sale of affordable cars to
the average citizen on the rationale that he/she can borrow an Audi or
Lexus or Mercedes from a generous neighbor anytime they need to drive
somewhere.

Chip Bearden
ASW 24 "JB"
USA

[toad]

On Feb 23, 6:28 am, Ian Strachan > wrote:
> > And what is so complicated in adding GPS altitiude as an IGC
> > recognized measurement ? Especially since GPS lat,lon is a
> > recognized. I am serious, please tell me.
>
> > Todd Smith
> > 3S- Hide quoted text -
>

.... snip usefull explanation of accuracy ...

> There is more, but the above summarises the reasons why IGC has, so
> far, not added GPS altitude to the Sporting Code where accurate
> measurements are required.
>
> Ian Strachan
> Lasham Gliding Centre, UK
> Chairman IGC GNSS Flight Recorder Approval Committee (GFAC)

Ian, thanks for that explanation.

My desire, even after hearing your clear explanation, to be able to
use GPS altitude comes from a willingness to allow "inaccurate"
measurements. Or more specifically to question, what level of
accuracy is truly needed for a Silver height gain claim ?

I have to read the report you referenced and learn what kind of
errors, but I would propose that even if the expected accuracy was as
large as 100m-200m, I would be comfortable allowing the Silver badge
to be claimed in the GPS altitude gain was greater that 1000m +
"expected max error".

It's my willingness to accept reduced accuracy for reduced cost that
would have me allow GPS altitude.

Again, this high tolerance for error would be for the lower level of
badges, not records.


A question for the group, what level of error (for badges) are you
comfortable with ?

Thanks again
Todd Smith

[Marc Ramsey[_2_]]

Chip Bearden wrote:
> On Feb 25, 12:53 pm, "PCool" > wrote:
>> Everyone agree on the fact that
>> the GPS Altitude is not accurate.
>
> Actually, what I took away from this discussion is that the GPS
> altitude is MORE accurate with regard to actual height above the
> ground but not necessarily equal to pressure altitude in the real
> world. So what I hear now is the Certified Flight Recorder crowd
> saying we shouldn't use GPS altitude even if it's more accurate, for
> the reason that it's not comparable with the way we've always
> evaluated badge and record claims in the past. This seems precisely
> the opposite argument used to justify GPS flight recorders in the
> first place: i.e., that their 2D positional accuracy was better so we
> simply *must* use it. :)

There are certainly some in this Certified Flight Recorder Crowd (like
myself, I guess) who think that GPS altitude, properly recorded and
evaluated, should be quite adequate for demonstrating that one has met
the requirements for at least a Gold badge.

> I agree airspace incursions are a different issue. But in the old
> days, we could only measure incursions on the Y axis (i.e. altitude)
> anyway. Would it be so bad if now we could only measure them on the X
> and Z axes (i.e., lat/long)? At most contests where I've flown
> recently, including US Nationals, that's been the case: i.e., we're
> not allowed to fly over or under most airspace that is restricted to
> gliders. Worst case, users of COTS receivers might have to self impose
> that condition or leave, say, a 1,000 ft. buffer

You're looking at this from a US perspective, in Europe there are lots
of places where if you don't fly under or over proscribed airspace, you
won't be going very far. Plus, I believe the floor of Class A is
somewhat lower over there.

> I'm not trying to make trouble but I'm genuinely baffled as to what is
> the problem. If GPS altitude is more accurate and COTS receivers are
> no more vulnerable to a determined hacker than, say, my Cambridge
> Model 20 (which I've had open several times), then why not allow them?
> Saying that the casual pilot can easily borrow an expensive Certified
> Flight Recorder from a more serious, more affluent club member on
> occasion is sort of like prohibiting the sale of affordable cars to
> the average citizen on the rationale that he/she can borrow an Audi or
> Lexus or Mercedes from a generous neighbor anytime they need to drive
> somewhere.

That is why it is so necessary to work with the IGC delegates. They are
the only ones who can change the rules...

Marc

[Marc Ramsey[_2_]]

PCool wrote:
> Thank you Mark, now it is all very clear to me, finally.
>
> I wish to do a summary of what I have understood, very simplified.
>
> What is Pressure Altitude for IGC standards
> It is the altitude calculated with an ICAO-ISA formula . You need a baro
> which has been calibrated at the factory, because the calibration is fixed
> at the time the recorder leaves the manufacturer (just like mechanical
> baro). The calibration is an important issue (exactly just like for the old
> good mechanical barographs). Once calibrated, you read a pressure value.
> You pass this value to a formula and get the ICAO-ISA altitude. In
> practice, QNE and ICAO-ISA may differ by some tens of meters, once
> calculated on the same value!
> You can revert the formula: starting from an ICAO-ISA altitude you can get
> the pressure.

You sort of lost me here 8^)

> What is Altitude for a Garmin and/or a GPS COTS
> The altitude measured by a GPS could be the real altitude over ground, but
> intrinsecally may contain geometric errors. Everyone agree on the fact that
> the GPS Altitude is not accurate.

Actually, GPS altitude is quite accurate at measuring actual height (to
within +/- 10 meters or so) *most* of the time. That last part is
important. Depending on lots of things, like bad satellite positions, a
wing or a rock blocking view of a critical satellite, the phase of the
moon, etc., GPS altitude can occasionally be hundreds of meters off. If
you take a longer term average, accuracy will normally be to within less
than a meter.

By contrast, pressure sensors are quite accurate and reliable at
measuring ISA pressure height (to within +/- a few meters or better,
below the tropopause), but can't accurately measure actual height. They
do not suffer from short term fluctuations and occasional wild
excursions like GPS altitude does (with the exception that some flight
recorder sensors will show large errors at low battery voltages).

> Some GPS like Garmin's use baro sensor to correct the GPS altitude, and
> vice-versa, in order to achieve maximum precision and obtain possibly the
> Real Altitude, above mean sea level. When we say "correct altitude" normally
> we refer to this.

Yes, to be more precise, when a Garmin is in auto-calibrate mode, the
pressure sensor is used to compensate for short term fluctuations in GPS
altitude, so you get the long term accuracy of GPS altitude, with the
short term stability and resolution of a pressure sensor.

> Why COTS' Altitude is not good for IGC badges
> The answer has nothing to do with precision. IGC requires to read ICAO
> Pressure-Altitude, not the real altitude.
> It is exactly the same altitude you may read on a paper from an old
> barograph.
> There could be little difference among the two, but in principle we are not
> talking about the same thing.

Correct, though some also argue that the short term accuracy of GPS
altitude is not good enough to allow verification of height gains and
loss of height. I believe there are ways to work around this, others don't.

> Of course a COTS could easily output an ICAO-ISA altitude, it's just a
> matter of using the formula and unselect any other corrections. The
> manufacturer could thus implement this feature, it is much easier than
> correcting and auto-calibrating GPS altitude.

This is true, but the pressure sensors need to have rather good
temperature compensation and long term stability, which may not be the
case with the sensors in consumer grade GPS receivers.

> BUT, but, the manufacturer should also provide a calibrated sensor at the
> factory.

They could, but remember, the market for glider pilots is insignificant
in comparison to the number of these units sold. It may simply not be
worth the added expense to the manufacturer.

> In other words: if three devices are standing at the same height, they
> should all read the same pressure value, say 747 mb.
> The garmin with sensor may say you are at 4750m , another COTS basing only
> on GPS may read 4680m, while the IGC may declare 4820m.

No quite, if the Garmin is auto-calibrating, it is reading actual
altitude (actually height above an ellipsoidal Earth model, but that is
another issue), just like the GPS-only unit (without the fluctuations).
So, the Garmin with sensor might read 5250m, GPS only might be 5230,
and IGC might read 4820m. They are all more or less correct, the IGC
unit is measuring something different. If the Garmin pressure sensor is
set to a proper fixed calibration, it will read the same as the IGC unit
(assuming adequate temperature compensation).

> Conclusion: without a pressure sensor no COTS can be used today as an
> alternative to IGC altitude loggers.
> And in any case, calibration is an issue.

At the moment, that is correct. The rest is up to the IGC.

Marc

[vontresc]

Just to throw some more fuel on the fire here. What about WAAS enabled
GPS. If the derived altitude is good enough for a quasi ILS approach
to 250' , shouldn't this be good enough for a flight logger?

Peter

[FreeFlight107[_2_]]

Sorry, but this is the sort of esoteric disscusion that actualy turns
me off to soaring.

IMHO either system is just fine, pick one and use it. Contests can do
what ever thay want, I won't participate due to several reasons. Badge
flying & CC is all I'm into.

From what I'm hearing I must use a Barograph in addition to the
expensive logger that I thought would do away with the 19th century
mechanical stuff of pressure chambers and mechanical camera pointing
that is not easy for a newcommer or non-decated sport flyier to do
correctly 100% of the time.

I would vote for the IGC to accept one system or the other, not
intermix them as is now done. If you're trying to measure your
position in relation to a forbidden airspace, you must use the one the
FAA or other National Agency requires, e.g.the altitude device on your
panel and disregard the others.

If you're in a contest you must use whatever the CD requires, right?

If you're going for badges or records you must use the system the
sanctioning body requires, right?

If you're going for club points you use what they require, even if
it's optically observed by the club VP of contest points.


Right now it appears we must use 19th century (or earlier) technology
for FAI altitude gains, expensive secure loggers for distance/time
measurments, and another divice for in-cockpit navigation.

If I were starting out in this sport, I'd choke on all those
requirements above and not go for badges, CC or contests becaue the
investment in dedicated equipment is too high, (I collected my devices
over the years as my paycheck could afford it).

If we really want to allow low cost entry to this sport, IMHO we
should allow the COTS GPS instruments for the badge flights as least,
I'm truely sorry that will destroy the market for dedciated Soaring
Instrument makers of high priced loggers, it's a shame, but that's
competition for you, happens everyday in my industry, (and I still
can't understand why they cost so much). Maybe it's just learning
curve, if so, we've learned, now move on.

End game: FAI/IGC pick a system, stick with it, allow older systems
for an economic phase in time (are we there yet?), and please try to
make it user friendly, espicialy new users friendly.

Wayne

[Marc Ramsey[_2_]]

vontresc wrote:
> Just to throw some more fuel on the fire here. What about WAAS enabled
> GPS. If the derived altitude is good enough for a quasi ILS approach
> to 250' , shouldn't this be good enough for a flight logger?

WAAS and other satellite-based augmentation systems like EGNOS (which is
not yet operational) are not available worldwide. IGC stands for
International Gliding Commission, which is why WAAS is not quite a good
enough solution at the moment...

Marc

[PCool]

>> Of course a COTS could easily output an ICAO-ISA altitude, it's just a
>> matter of using the formula and unselect any other corrections. The
>> manufacturer could thus implement this feature, it is much easier than
>> correcting and auto-calibrating GPS altitude.
>
> This is true, but the pressure sensors need to have rather good
> temperature compensation and long term stability, which may not be the
> case with the sensors in consumer grade GPS receivers.
>


Sure, I forgot. The sensor of course need to be not only calibrated but also
compensated against temperature.
I think that latest Garmin have a temperature sensor for this, but not old
ones.

However, I feel that nowadays "consumer grade GPS" sold in dozen of
thousands of units at a price of 500-600$ (in europe much more) cannot be
called cheap and represent the state-of-the-art in terms of technology.
There are also low cost gps units, and you get what you pay for, exactly as
with LCD screens and computers, or a pair of glasses made in china.
So I would'nt bet that a good Garmin prices at 500$ is inferior to any
"professional" altimeter or gps ot both. Au contraire, it probably is better
being more recent.
Let's not forget that the cost of an Interseema sensor , used in GP941 and
many other I guess, is below 20$ to the common user.

In the end, I feel that IGC will not change the Code to make COTS usable for
badges. They should change the rule about what is altitude, abandoning
ICAO-ISA which is a standard.

Maybe with a petition?

Thanks again Mark! Paolo

[toad]

On Feb 25, 1:36 pm, Marc Ramsey > wrote:

....snip...

> There are certainly some in this Certified Flight Recorder Crowd (like
> myself, I guess) who think that GPS altitude, properly recorded and
> evaluated, should be quite adequate for demonstrating that one has met
> the requirements for at least a Gold badge.

You had me convinced otherwise.

....snip...

> That is why it is so necessary to work with the IGC delegates. They are
> the only ones who can change the rules...
>
> Marc

I guess what I thought was going on here was us discussing whether we
should try to convince the IGC to allow GPS altitude or not. Actually
getting the ICG to change wasn't my focus. If somebody had given a
reason that GPS altitude was just not gonna work, I would drop the
question.

Todd

[Cats]

On Feb 25, 8:00*pm, vontresc > wrote:
> Just to throw some more fuel on the fire here. What about WAAS enabled
> GPS. If the derived altitude is good enough for a quasi ILS approach
> to 250' , shouldn't this be good enough for a flight logger?

I don't think WAAS enabled GPS is available throughout the gliding
world. Whatever solutions are acceptable to the IGC have to be
available anywhere that people are flying, not just in the US:

http://www8.garmin.com/aboutGPS/waas.html

Who benefits from WAAS?

Currently, WAAS satellite coverage is only available in North America.
There are no ground reference stations in South America, so even
though GPS users there can receive WAAS, the signal has not been
corrected and thus would not improve the accuracy of their unit. For
some users in the U.S., the position of the satellites over the
equator makes it difficult to receive the signals when trees or
mountains obstruct the view of the horizon. WAAS signal reception is
ideal for open land and marine applications. WAAS provides extended
coverage both inland and offshore compared to the land-based DGPS
(differential GPS) system. Another benefit of WAAS is that it does not
require additional receiving equipment, while DGPS does.

Other governments are developing similar satellite-based differential
systems. In Asia, it's the Japanese Multi-Functional Satellite
Augmentation System (MSAS), while Europe has the Euro Geostationary
Navigation Overlay Service (EGNOS). Eventually, GPS users around the
world will have access to precise position data using these and other
compatible systems.

[nimbusgb]

On 25 Feb, 20:04, FreeFlight107 > wrote:
> Sorry, but this is the sort of esoteric disscusion that actualy turns
> me off to soaring.
>
> IMHO either system is just fine, pick one and use it. Contests can do
> what ever thay want, I won't participate due to several reasons. Badge
> flying & CC is all I'm into.
>
> From what I'm hearing I must use a Barograph in addition to the
> expensive logger that I thought would do away with the 19th century
> mechanical stuff of pressure chambers and mechanical camera pointing
> that is not easy for a newcommer or non-decated sport flyier to do
> correctly 100% of the time.
>

If you have an IGC full flight data recorder ( most of us call then
rloggers ) then it can be used, stand alone, for anything up to and
including world records without the need for a barograph or anything
else.

Provided of course that the recorder is igc certified to that level -
most are.

[Eric Greenwell]

FreeFlight107 wrote:
> Sorry, but this is the sort of esoteric disscusion that actualy turns
> me off to soaring.
>
> IMHO either system is just fine, pick one and use it. Contests can do
> what ever thay want, I won't participate due to several reasons. Badge
> flying & CC is all I'm into.

A system has been chosen, and we are using it. The discussion is about
increasing the choices to lower costs.

>
> From what I'm hearing I must use a Barograph in addition to the
> expensive logger that I thought would do away with the 19th century
> mechanical stuff of pressure chambers and mechanical camera pointing
> that is not easy for a newcommer or non-decated sport flyier to do
> correctly 100% of the time.

If you use an "expensive" logger (meaning, I assume, a "secure" IGC
logger good for badges and records), you will NOT need to use a
barograph. Get one of these, and you skip the esoteric discussion going
on here, and enjoy all the benefits of the best (if more expensive)
system. It's what I have, an it's great for badges and records, making
the pilot's job and the observer's job about as easy as possible. I'm
not bothered by the extra $600 it cost me over the COTS units being
discussed, as it continues to deliver it's advantages year after year.

snip

> Right now it appears we must use 19th century (or earlier) technology
> for FAI altitude gains, expensive secure loggers for distance/time
> measurments, and another divice for in-cockpit navigation.

To repeat, get an IGC secure logger, and you can use it for everything,
including altitude gains. The navigation device can may be part of some
loggers, you can use a device that connects to it (e.g., and Ipaq
running See You Mobile, Winpilot, etc), or you can use an entirely
separate device (even a paper map). Navigation is a separate issue from
flight recording.

> If I were starting out in this sport, I'd choke on all those
> requirements above and not go for badges, CC or contests becaue the
> investment in dedicated equipment is too high, (I collected my devices
> over the years as my paycheck could afford it).

And this discussion is aimed at reducing these costs you complain about!
I'm surprised it "turns you off".

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[[email protected]]

Let's see:
1) IGC Flight recorders are expensive because the market is small
2) No manufacturer is making any profit, some have left the business
(and their customers)
3) The market is almost saturated
4) If COTS receivers are accepted, half (or more) of the shrinking
market evaporates

Guess what will happen to the price of IGC approved flight recorders.

Beware of the law of unintended consequences.

[hans]

Hi nimbusgb schrieb:

> At the time that flight recorders were just getting going a LOT of
> consultation was done and many, many hours were spent by people like
> Tim for zero reward apart from delivering an acceptable methodology
> for improving and simplifying the flight verification procedures. At
> the time Cambridge were the only manufacturers of any sort of flight
> recorder following their early demos in Sweden in 93 and New Zealand
> in 95. Even they did not get things all their way in the ensuing
> regulation changes. In this day and age and the track record of
> American companies it still surprises me that they didn't tie the
> whole idea up in patents which might have had us paying 5 times the
> current price for flight recorders today.

There where other companies arrount, that did flight recording with GPS
for quite a long time, at the time CAI promoted the flight recording for
documentation in central competitions. So there was no way to
patent it.

[nimbusgb]

>
> There where other companies around, that did flight recording with GPS
> for quite a long time, at the time CAI promoted the flight recording for
> documentation in central competitions. So there was no way to
> patent it.

That never seemed to stop an American company before! :) :) :)

[5Z]

On Feb 28, 1:51 am, nimbusgb > wrote:
> > There where other companies around, that did flight recording with GPS
> > for quite a long time, at the time CAI promoted the flight recording for
> > documentation in central competitions. So there was no way to
> > patent it.
>
> That never seemed to stop an American company before! :) :) :)

Nor a British one... http://www.wired.com/politics/law/news/2000/06/37095

:-)

[Papa3]

On Feb 28, 1:15*am, wrote:
> Let's see:
> 1) IGC Flight recorders are expensive because the market is small
> 2) No manufacturer is making any profit, some have left the business
> (and their customers)
> 3) The market is almost saturated
> 4) If COTS receivers are accepted, half (or more) of the shrinking
> market evaporates
>
> Guess what will happen to the price of IGC approved flight recorders.
>
> Beware of the law of unintended consequences.

What do you mean "unintended" :-)

One of the points that I've stressed all along is that we need to work
on an approach to de-risk our current reliance on what has been a
cottage industry. The fact that an increasing number of people are
finding an outlet for their competitive spirit in the form of the OLC
is a strong indicator that the "market" will dictate where we are
going. The fact that OLC pilots and competition pilots in many
countries (e.g. in the US up to the national level) can already
compete using COTS recorders means that they are here to stay. At
the same time, there are new manufucturers of IGC-approved loggers
coming on line with much greater resources (i.e. not reliant on the
relatively small gliding market) who have much lower cost
structures.

I'm sure many people know that Cambridge has been barely limping along
for years now (what was the last major product release?), and if they
couldn't survive, what leads you to believe that the others are far
behind?

P3

[[email protected]]

On Feb 25, 7:47*am, "PCool" > wrote:
> Thanks Marc,
>
> is it correct to say that the Pressure Altitude is an altitude calculated
> starting from a pressure value, following a sort-of a rule as for ICAO-ISA ?
> I guess official IGC loggers read the exact pressure as garmins and suunto
> watches (!) and then they apply some calculations and name this result as
> "altitude".
> Do they do this without looking at what the GPS say?? Not even for an hint?
>
> What is the formula used by all IGC loggers for doing this, then?
>
> It's beyond my comprehension why if we are talking about pressure which is
> always measured in the same way (right?) then this value has different
> meanings and cannot be simply converted like with QNE-QNH-QFE.
> ICAO-ISA is sort of a more complicated QNE, right? (question!)
>
> On garmins you have a pressure sensor just like on a Colibrì, then this
> sensor is used to compensate the gps and vice-versa, according to the patent
> they have registered. By the way Marc could you understand anything useful
> out of it?
>
> After 4 years there are again the same questions on this matter so I guess
> it's not very clear to everybody (me too).
>
> thanks!
> Paolo
>
> "Marc Ramsey" > ha scritto nel . prodigy.net...
>
>
>
>
>
> > Once again, pressure altitude and GPS altitude measure two different
> > things using the same units. *Because we like to fly when there is a
> > non-standard temperature lapse rate, there is almost always noticeable
> > pressure altitude error above a few thousand feet AGL. *If an optical
> > start gate is showing the actual heights, most gliders will appear to be
> > starting high, since the altimeters are reading low, and the validity of
> > the start is determined from the recorded pressure altitude. *Those pilots
> > who are recording only GPS altitude (GPS handhelds, etc.) need to be
> > careful, as they start will be scored based on actual height, which means
> > they have to start lower. *They need to be watching the GPS display,
> > rather then the altimeter, when they are flirting with the top of the
> > start cylinder.
>
> >> Do the experts maintain that GPS altitude is bad because (a) it
> >> DOESN'T have the errors inherent in pressure altitude or (b) because
> >> its precision isn't good enough? It seems like I've seen both
> >> positions on this forum.
>
> > As you know, experts generally maintain whatever favors their position.
> > Look at it this way, GPS altitude is more accurate at measuring actual
> > height, pressure altitude is more accurate at measuring, well, pressure
> > altitude. *Since one function of the flight recorder is to detect and
> > penalize airspace incursions, pressure altitude will continue to be a
> > consideration, no matter what else happens. *Some of the other air sports,
> > like ballooning, have already switched over to using actual height, they
> > use sounding data and software to convert to/from pressure altitude as
> > needed.
>
> > Marc- Hide quoted text -
>
> - Show quoted text -

I think that to a large degree, the requirement to use pressure
altitude may be related to the reason the FAA insists on using it for
altitude deconfliction. Pretty much every plane out there has a
pressure altimeter.
I wonder if the GPS altitude anomolies are related to antenna position
while circling? That, IMO, would be valid. Otherwise, GPS, even
relatively low end GPS yields vastly more consistant altitudes than
pressure sensors.

[vontresc]

I saw somewhere that the IGC was meeting from the 29th to the 1st.
Have they released any ino on what was decided yet?

Pete