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"