IGC File / Flight-track Analysis

Hi All,

I'm working on a project that I can't talk about much, but I was
hoping to prevail upon some experts here. I need to analyze some IGC
files in my project, and try to use the data to determine the behavior
of the glider.

As I understand it, the bulk of the IGC file is just a series of time-
stamped position & altitude fixes. So to determine an aircraft's
heading (ground-track to be more precise, since we're referencing GPS
coordinates), I have to use pairs of position-fixes to come up with a
direction & velocity vector... Yes?

OK, now here's where it gets a little tricky: How to I make the leap
from those raw vectors to determining behavior? For example, you can
signal your release from tow by executing a sharp 360-degree turn.
Its easy enough to look at a few vectors in a row and as long as they
keep angling off to the same side (relative to the previous vector)
then I can consider the glider in a continuous turn. As long as the
continuous turn takes us past 360 degrees from the ground-track/
heading at the beginning of the turn, we're OK - right? But what
happens if the glider catches a gust of wind that slews the tail
momentarily or causes the glider to slip? What is my "fudge factor"
for these things and how do I reasonably account for them?

There are some other oddities that I'm unsure how to account for (or
if I even need to) - like: How do I deal with a wind-drift that's
causing the glider's absolute position to be offset?

I'm a programmer & IT person by day, but my work is keeping me
terribly busy and I've never had to do much in terms of pathing or
vector analysis - so this stuff is harder for me than it should be
right now. :-P Any help would be much appreciated!

Thanks, take care,

--Noel

On Jan 21, 3:56*am, "noel.wade" wrote:
Hi All,

I'm working on a project that I can't talk about much, but I was
hoping to prevail upon some experts here. *I need to analyze some IGC
files in my project, and try to use the data to determine the behavior
of the glider.

As I understand it, the bulk of the IGC file is just a series of time-
stamped position & altitude fixes. *So to determine an aircraft's
heading (ground-track to be more precise, since we're referencing GPS
coordinates), I have to use pairs of position-fixes to come up with a
direction & velocity vector... Yes?

Some flight recorders include the track information in the
IGC file via optional additions to the B records.
ILEC SN10 does this.

In any case, beware that the position and track as reported by
the GPS are the output of smoothing Kalman filters. Also, there
will be occasional discontinuities so take care to look for and
ignore these or your code will blow up. I have example log
files where time goes backwards, and positions jumping from
Montana into the North Atlantic. You'll see a "bad fix" count
in any of the analysis programs...

Be sure your intended use of the data can tolerate its
"features"...

OK, now here's where it gets a little tricky: *How to I make the leap
from those raw vectors to determining behavior? *For example, you can
signal your release from tow by executing a sharp 360-degree turn.
Its easy enough to look at a few vectors in a row and as long as they
keep angling off to the same side (relative to the previous vector)
then I can consider the glider in a continuous turn. *As long as the
continuous turn takes us past 360 degrees from the ground-track/
heading at the beginning of the turn, we're OK - right? *But what
happens if the glider catches a gust of wind that slews the tail
momentarily or causes the glider to slip? *What is my "fudge factor"
for these things and how do I reasonably account for them?

There are some other oddities that I'm unsure how to account for (or
if I even need to) - like: *How do I deal with a wind-drift that's
causing the glider's absolute position to be offset?

You could just calculate the wind.
That's what we do in the ILEC SN10 ;-)

I'm a programmer & IT person by day, but my work is keeping me
terribly busy and I've never had to do much in terms of pathing or
vector analysis - so this stuff is harder for me than it should be
right now. :-P *Any help would be much appreciated!

Sounds like you need to hit the books ;-)

Thanks, take care,

--Noel

Hope this helps !
Best Regards, Dave "YO electric"

noel.wade wrote:
Hi All,

I'm working on a project that I can't talk about much, but I was
hoping to prevail upon some experts here. I need to analyze some IGC
files in my project, and try to use the data to determine the behavior
of the glider.
There are a number of programs that do this, such as SeeYou, simulator
software (Condor?), even commercial programs that reconstruct a flight
from gps data for accident and other investigations. T2T (track to
thermal) picks out thermals from the data. Have you investigated
acquiring one of these programs, or getting them to slice of a piece of
it for your purposes?

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

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

On Jan 21, 8:00*pm, Eric Greenwell wrote:

There are a number of programs that do this, such as SeeYou, simulator
software (Condor?), even commercial programs that reconstruct a flight
from gps data for accident and other investigations. T2T (track to

Eric -

Yes I have. The catch is that this project isn't mine; I'm
volunteering my time for it. And the people I'm working with don't
want the end-result to be tied to any licensing fees or restrictions
on use of the code.
*sigh* *shrug*

Thanks all,

--Noel

noel.wade wrote:
On Jan 21, 8:00 pm, Eric Greenwell wrote:

There are a number of programs that do this, such as SeeYou, simulator
software (Condor?), even commercial programs that reconstruct a flight
from gps data for accident and other investigations. T2T (track to

Eric -

Yes I have. The catch is that this project isn't mine; I'm
volunteering my time for it. And the people I'm working with don't
want the end-result to be tied to any licensing fees or restrictions
on use of the code.
*sigh* *shrug*

Thanks all,

--Noel

XC Soar is Open Source, which might work if the GPL restrictions
wouldn't affect the exploitation of the project (this would require you
to make any modified XC Soar code modules available under the GPS terms,
but not interfacing modules which would stay proprietary).

On Jan 22, 3:05*am, Chris Reed wrote:
noel.wade wrote:
On Jan 21, 8:00 pm, Eric Greenwell wrote:

There are a number of programs that do this, such as SeeYou, simulator
software (Condor?), even commercial programs that reconstruct a flight
from gps data for accident and other investigations. T2T (track to

Eric -

Yes I have. *The catch is that this project isn't mine; I'm
volunteering my time for it. *And the people I'm working with don't
want the end-result to be tied to any licensing fees or restrictions
on use of the code.
*sigh* *shrug*

Thanks all,

--Noel

XC Soar is Open Source, which might work if the GPL restrictions
wouldn't affect the exploitation of the project (this would require you
to make any modified XC Soar code modules available under the GPS terms,
but not *interfacing modules which would stay proprietary).

I'd contact the Aerospace Engineering department at a university near
you. Most graduate programs and some undergraduate ones have analytic
tools they use to do optimal estimation for a state-space
representation of aircraft. To do some of the things you are asking
about I suspect you'd need a full 6 degree of freedom model. Depending
on what the inputs are, you may not be able to fully estimate the
aircraft state - there would be too many unknowns. For instance,
because you don't have attitude information (none of the Euler
angles), you wouldn't be able to cleanly distinguish between gusts
displacing the aircraft and control inputs. You would likely need to
assume coordinated flight and no wind gusts. Some simple Kalman
filters should help, as Dave says.

9B

On Jan 22, 7:10*am, Andy wrote:
On Jan 22, 3:05*am, Chris Reed wrote:



noel.wade wrote:
On Jan 21, 8:00 pm, Eric Greenwell wrote:

There are a number of programs that do this, such as SeeYou, simulator
software (Condor?), even commercial programs that reconstruct a flight
from gps data for accident and other investigations. T2T (track to

Eric -

Yes I have. *The catch is that this project isn't mine; I'm
volunteering my time for it. *And the people I'm working with don't
want the end-result to be tied to any licensing fees or restrictions
on use of the code.
*sigh* *shrug*

Thanks all,

--Noel

XC Soar is Open Source, which might work if the GPL restrictions
wouldn't affect the exploitation of the project (this would require you
to make any modified XC Soar code modules available under the GPS terms,
but not *interfacing modules which would stay proprietary).

I'd contact the Aerospace Engineering department at a university near
you. *Most graduate programs and some undergraduate ones have analytic
tools they use to do optimal estimation for a state-space
representation of aircraft. To do some of the things you are asking
about I suspect you'd need a full 6 degree of freedom model. Depending
on what the inputs are, you may not be able to fully estimate the
aircraft state - there would be too many unknowns. For instance,
because you don't have attitude information (none of the Euler
angles), you wouldn't be able to cleanly distinguish between gusts
displacing the aircraft and control inputs. You would likely need to
assume coordinated flight and no wind gusts. Some simple Kalman
filters should help, as Dave says.

9B

Um, depending on what he's trying to do, the Kalman filters
in the GPS could make life very difficult. Adding another
Kalman filter in back of the filter already in the GPS engine
is not likely to help. And every brand of GPS (and potentially
every software revision of the same brand) may have different
filtering.

Here's an experiment conducted a few times, with a GPS
engine in a car:
Drive at high speed
Disable the antenna
Slow rapidly and turn 90 degrees
Speed up
Enable antenna

What do you think the GPS output shows ?

Hope that helps clarify the problem,
Best Regards, Dave "YO electric"