Accuracy of GPS in Garmin 430/530

"Will" wrote:
It may just be personal preference, but I see a lot of value in user
interfaces that make the data quality a primary display attribute at all
times. That way I not only know I have a GPS signal, but I can quickly
assess the quality of the signal. I see value in making this more than just
a binary state ("good enough for the FAA" GPS signal quality / "not good
enough for the FAA" GPS signal quality). Possibly that data could be
colored or made to blink in situations where integrity is compromised
sufficiently.

I disagree. We already have information overload. A binary "go/no-go" is
exactly what you want. If I told you that the SNR from satellite 17 was
down 6dB, what would you do with that information?

RAIM factors in signal strength as well as satellite geometry. To get a
good fix, you need to be getting a good signal from 4 satellites positioned
appropriately in both azimuth and elevation. Figuring out if the signal
strength and geometry is "good enough" is not the kind of problem people
can do in their heads.

Roy Smith wrote:
"Will" wrote:

It may just be personal preference, but I see a lot of value in user
interfaces that make the data quality a primary display attribute at all
times. That way I not only know I have a GPS signal, but I can quickly
assess the quality of the signal. I see value in making this more than just
a binary state ("good enough for the FAA" GPS signal quality / "not good
enough for the FAA" GPS signal quality). Possibly that data could be
colored or made to blink in situations where integrity is compromised
sufficiently.


I disagree. We already have information overload. A binary "go/no-go" is
exactly what you want. If I told you that the SNR from satellite 17 was
down 6dB, what would you do with that information?

RAIM factors in signal strength as well as satellite geometry. To get a
good fix, you need to be getting a good signal from 4 satellites positioned
appropriately in both azimuth and elevation. Figuring out if the signal
strength and geometry is "good enough" is not the kind of problem people
can do in their heads.
I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength. I've never felt the need to run thru the 430/530 pages
to find a similar page but would not be surprised to find it buried in
there somewhere. To answer the OP's question it's there you just need
to read the manual to find which sub-menu it's on. If he's using a
non-aviation unit then all bets are off but again I would think it would
be there somewhere. Also on the units I use regularly the airplane icon
flashs on the main display when the signal is lost ala a pseudo RAIM
indicator

John Theune wrote:
..

I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength.

Page 4 of the nav section.

On 04/25/06 05:03, John Theune wrote:
Roy Smith wrote:
"Will" wrote:

It may just be personal preference, but I see a lot of value in user
interfaces that make the data quality a primary display attribute at all
times. That way I not only know I have a GPS signal, but I can quickly
assess the quality of the signal. I see value in making this more than just
a binary state ("good enough for the FAA" GPS signal quality / "not good
enough for the FAA" GPS signal quality). Possibly that data could be
colored or made to blink in situations where integrity is compromised
sufficiently.


I disagree. We already have information overload. A binary "go/no-go" is
exactly what you want. If I told you that the SNR from satellite 17 was
down 6dB, what would you do with that information?

RAIM factors in signal strength as well as satellite geometry. To get a
good fix, you need to be getting a good signal from 4 satellites positioned
appropriately in both azimuth and elevation. Figuring out if the signal
strength and geometry is "good enough" is not the kind of problem people
can do in their heads.
I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength. I've never felt the need to run thru the 430/530 pages
to find a similar page but would not be surprised to find it buried in
there somewhere. To answer the OP's question it's there you just need
to read the manual to find which sub-menu it's on. If he's using a
non-aviation unit then all bets are off but again I would think it would
be there somewhere. Also on the units I use regularly the airplane icon
flashs on the main display when the signal is lost ala a pseudo RAIM
indicator

The OP was asking why this can't be displayed on the main page...

You snipped it from your response. Here it is:

Is there any way to have the Garmin 430/530 put its current display accuracy
on the primary display as an ongoing statistic, based on the number of
satellites in view?




--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

"John Theune" wrote in message
news:Udo3g.5009$bU6.3635@trnddc06...
I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength. I've never felt the need to run thru the 430/530 pages
to find a similar page but would not be surprised to find it buried in
there somewhere. To answer the OP's question it's there you just need
to read the manual to find which sub-menu it's on. If he's using a
non-aviation unit then all bets are off but again I would think it would
be there somewhere. Also on the units I use regularly the airplane icon
flashs on the main display when the signal is lost ala a pseudo RAIM
indicator

You are right all GPS software usually implements a satellite signal page.
It's not in any way shape or form what I asked for.

I want the GPS to take all of the inputs for number of satellites and signal
strength and derive from that just two integers:

1) Number of feet/meters of horizontal accuracy, within some confidence
interval (e.g., 99.95%)

2) Number of feet/meters of vertical accuracy, within some confidence
interval (e.g., 99.95%)

Those two numbers could become optional numbers for the primary display.
No one is forcing anyone to use them. If you want to simply trust the
instrument to give you a go-nogo decision, it's your life and if you feel
that is safe it's a free world (as long as you follow FAA rules ) so be
my guest.

For my personal taste, I understand that a GPS display is always an illusion
subject to different levels of inaccuracy. I am sensitive to the
difference between a display that is showing me accuracy to 10 ft, 100 ft,
or 1000 ft. In the original posted example the GPS was off target by more
than 5000 ft. Nothing on the original display gave me any clue that this
was the case. The two numbers I am asking for would communicate quite
succinctly that no one should rely on the display for anything other than
the most gross kind of positioning.

While I would love to see the feature I am looking for in any FAA-compliant
instrument like a Garmin 530, I think the feature becomes most critical in
non-FAA compliant GPS devices/software. The authors of such packages
cannot control the quality of the satellite antenna, or mounting, and
substandard GPS reception is probably a routine thing for PDA based GPS
devices/software. So finding a succinct way to communicate the accuracy of
the current signal in numbers that mean something to any user becomes quite
important. Making people look at satellite maps and signal strength seems
like a pure engineering exercise, and it doesn't collapse the input data
into a useful form.

--
Will

Will wrote:
"John Theune" wrote in message
news:Udo3g.5009$bU6.3635@trnddc06...

I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength. I've never felt the need to run thru the 430/530 pages
to find a similar page but would not be surprised to find it buried in
there somewhere. To answer the OP's question it's there you just need
to read the manual to find which sub-menu it's on. If he's using a
non-aviation unit then all bets are off but again I would think it would
be there somewhere. Also on the units I use regularly the airplane icon
flashs on the main display when the signal is lost ala a pseudo RAIM
indicator


You are right all GPS software usually implements a satellite signal page.
It's not in any way shape or form what I asked for.

I want the GPS to take all of the inputs for number of satellites and signal
strength and derive from that just two integers:

1) Number of feet/meters of horizontal accuracy, within some confidence
interval (e.g., 99.95%)

2) Number of feet/meters of vertical accuracy, within some confidence
interval (e.g., 99.95%)

Those two numbers could become optional numbers for the primary display.
No one is forcing anyone to use them. If you want to simply trust the
instrument to give you a go-nogo decision, it's your life and if you feel
that is safe it's a free world (as long as you follow FAA rules ) so be
my guest.

For my personal taste, I understand that a GPS display is always an illusion
subject to different levels of inaccuracy. I am sensitive to the
difference between a display that is showing me accuracy to 10 ft, 100 ft,
or 1000 ft. In the original posted example the GPS was off target by more
than 5000 ft. Nothing on the original display gave me any clue that this
was the case. The two numbers I am asking for would communicate quite
succinctly that no one should rely on the display for anything other than
the most gross kind of positioning.

While I would love to see the feature I am looking for in any FAA-compliant
instrument like a Garmin 530, I think the feature becomes most critical in
non-FAA compliant GPS devices/software. The authors of such packages
cannot control the quality of the satellite antenna, or mounting, and
substandard GPS reception is probably a routine thing for PDA based GPS
devices/software. So finding a succinct way to communicate the accuracy of
the current signal in numbers that mean something to any user becomes quite
important. Making people look at satellite maps and signal strength seems
like a pure engineering exercise, and it doesn't collapse the input data
into a useful form.

And right on that same page for the Lowrance unit is the EPE ( Estimated
Probability of Error ) in feet for the current location. The EPE is for
horizontal accuracy as the vertical accuracy is mostly meaningless for
GPS as they can only give you vertical guidance from a perfect sphere
and the earth does not quite fit that. vertical accuracy would require
the GPS to have a complete model of the earth elevation and coralate
that to the horizontal location so as to determine the actual vertical
location vs calculated position. Now I spent a few moments messing with
my unit and found that I can place the EPE on the main map page along
side course, heading , speed and so forth. If you want to know more I
suggest you look at the manual for your system.

Read the TSO and then read the description of RAIM other
accuracy monitoring software built into the unit.



--
James H. Macklin
ATP,CFI,A&P

"Will" wrote in message
...
|
| "John Theune" wrote in message
| news:Udo3g.5009$bU6.3635@trnddc06...
| I'm somewhat surprised that no one has mentioned that
both the Garmin
| and Lowrance units that I'm familiar with have a page
for satelitte
| signal strength. I've never felt the need to run thru
the 430/530 pages
| to find a similar page but would not be surprised to
find it buried in
| there somewhere. To answer the OP's question it's there
you just need
| to read the manual to find which sub-menu it's on. If
he's using a
| non-aviation unit then all bets are off but again I
would think it would
| be there somewhere. Also on the units I use regularly
the airplane icon
| flashs on the main display when the signal is lost ala a
pseudo RAIM
| indicator
|
| You are right all GPS software usually implements a
satellite signal page.
| It's not in any way shape or form what I asked for.
|
| I want the GPS to take all of the inputs for number of
satellites and signal
| strength and derive from that just two integers:
|
| 1) Number of feet/meters of horizontal accuracy, within
some confidence
| interval (e.g., 99.95%)
|
| 2) Number of feet/meters of vertical accuracy, within some
confidence
| interval (e.g., 99.95%)
|
| Those two numbers could become optional numbers for the
primary display.
| No one is forcing anyone to use them. If you want to
simply trust the
| instrument to give you a go-nogo decision, it's your life
and if you feel
| that is safe it's a free world (as long as you follow FAA
rules ) so be
| my guest.
|
| For my personal taste, I understand that a GPS display is
always an illusion
| subject to different levels of inaccuracy. I am
sensitive to the
| difference between a display that is showing me accuracy
to 10 ft, 100 ft,
| or 1000 ft. In the original posted example the GPS was
off target by more
| than 5000 ft. Nothing on the original display gave me
any clue that this
| was the case. The two numbers I am asking for would
communicate quite
| succinctly that no one should rely on the display for
anything other than
| the most gross kind of positioning.
|
| While I would love to see the feature I am looking for in
any FAA-compliant
| instrument like a Garmin 530, I think the feature becomes
most critical in
| non-FAA compliant GPS devices/software. The authors of
such packages
| cannot control the quality of the satellite antenna, or
mounting, and
| substandard GPS reception is probably a routine thing for
PDA based GPS
| devices/software. So finding a succinct way to
communicate the accuracy of
| the current signal in numbers that mean something to any
user becomes quite
| important. Making people look at satellite maps and
signal strength seems
| like a pure engineering exercise, and it doesn't collapse
the input data
| into a useful form.
|
| --
| Will
|
|
|
|

You will never get the display you are looking for in a handheld device.
IMHO handhelds will never have RAIM.

Bob Gardner

"Will" wrote in message
...

"John Theune" wrote in message
news:Udo3g.5009$bU6.3635@trnddc06...
I'm somewhat surprised that no one has mentioned that both the Garmin
and Lowrance units that I'm familiar with have a page for satelitte
signal strength. I've never felt the need to run thru the 430/530 pages
to find a similar page but would not be surprised to find it buried in
there somewhere. To answer the OP's question it's there you just need
to read the manual to find which sub-menu it's on. If he's using a
non-aviation unit then all bets are off but again I would think it would
be there somewhere. Also on the units I use regularly the airplane icon
flashs on the main display when the signal is lost ala a pseudo RAIM
indicator

You are right all GPS software usually implements a satellite signal page.
It's not in any way shape or form what I asked for.

I want the GPS to take all of the inputs for number of satellites and
signal
strength and derive from that just two integers:

1) Number of feet/meters of horizontal accuracy, within some confidence
interval (e.g., 99.95%)

2) Number of feet/meters of vertical accuracy, within some confidence
interval (e.g., 99.95%)

Those two numbers could become optional numbers for the primary display.
No one is forcing anyone to use them. If you want to simply trust the
instrument to give you a go-nogo decision, it's your life and if you feel
that is safe it's a free world (as long as you follow FAA rules ) so
be
my guest.

For my personal taste, I understand that a GPS display is always an
illusion
subject to different levels of inaccuracy. I am sensitive to the
difference between a display that is showing me accuracy to 10 ft, 100 ft,
or 1000 ft. In the original posted example the GPS was off target by
more
than 5000 ft. Nothing on the original display gave me any clue that this
was the case. The two numbers I am asking for would communicate quite
succinctly that no one should rely on the display for anything other than
the most gross kind of positioning.

While I would love to see the feature I am looking for in any
FAA-compliant
instrument like a Garmin 530, I think the feature becomes most critical in
non-FAA compliant GPS devices/software. The authors of such packages
cannot control the quality of the satellite antenna, or mounting, and
substandard GPS reception is probably a routine thing for PDA based GPS
devices/software. So finding a succinct way to communicate the accuracy
of
the current signal in numbers that mean something to any user becomes
quite
important. Making people look at satellite maps and signal strength
seems
like a pure engineering exercise, and it doesn't collapse the input data
into a useful form.

--
Will

Will,

I want the GPS to take all of the inputs for number of satellites and signal
strength and derive from that just two integers:


What you want is in the values for PDOP, VDOP and HDOP - and EPE.

--
Thomas Borchert (EDDH)

"Roy Smith" wrote in message
...
I disagree. We already have information overload. A binary "go/no-go" is
exactly what you want. If I told you that the SNR from satellite 17 was
down 6dB, what would you do with that information?

That's not useful information the way you present it. I want conclusions
and not data. Specifically I want to know the number of feet/meters of
accuracy of my current position, that's all. If my current accuracy is 10
ft vertical versus 100 ft vertical versus 1000 ft vertical, that means
something to me about how much trust I should put in the GPS display.

--
Will