missing gps fixes after upload

After uploading my latest flight to the OLC, the server told me that
the file was invalid due to a large time gap between GPS fixes. Both
my secure *.cai and *.igc files show no such gap; it only appears on
the OLC trace. I've sent an e-mail to the OLC to see what they think,
but I'm curious to see if anybody else has had this problem, and what
they did to fix it. Thanks in advance!

Chris 'CF'
OLC-USA
2006-12-04
El Paso Soaring Society
Cambridge GPS-NAV Model 20
SeeYou v3.5a (Cambridge patch installed)
Previous flights uploaded successfully

There is a program that breaks down the fixes and times have you run the IGC
file through that.

How have you checked the IGC file for gaps? By loading it into SeeYou?
SeeYou will automatically skip over an out of order fix when
displaying a flight. My guess is if you checked the IGC file in detail
there is an out of order record.

A regular fix will look like this:
B1929283318443N11641991WA0121001246000000000000

A bad fix will probably look like this:
B1929323318500N11642046WV0121701255000000000000
Note the 'V' after the 'W' , instead of an 'A'.





charlie foxtrot wrote:
After uploading my latest flight to the OLC, the server told me that
the file was invalid due to a large time gap between GPS fixes. Both
my secure *.cai and *.igc files show no such gap; it only appears on
the OLC trace. I've sent an e-mail to the OLC to see what they think,
but I'm curious to see if anybody else has had this problem, and what
they did to fix it. Thanks in advance!

Chris 'CF'
OLC-USA
2006-12-04
El Paso Soaring Society
Cambridge GPS-NAV Model 20
SeeYou v3.5a (Cambridge patch installed)
Previous flights uploaded successfully

What sort of recorder (Manufacturer /exact model)?

Did the IGC file concerned pass the appropriate VALIDATION test program
(available free from the IGC GNSS web pages)?

Has the IGC file concerned been posted where others can have a look at
it?

Ian Strachan
Lasham Gliding Centre, UK

In my last posting, sorry, I missed that the recorder was a Cambridge
20 because you put this under your name rather than in the text.

The problems associated with the three legacy Cambridge models 10, 20
and 25 when used for OLC flights, have been extensively discussed on
this newsroup. In terms of using the free VALI-CAM.exe program, this
only works with the binary CAI file and not with the IGC file that is
derived from it. And if you alter the IGC file, the VALI program will
register it as invalid because it has been altered.

By all means email the files (CAI and IGC) to me and I will look at
them with analysis software that enables every fix to be looked at in
detail. Some analysis software uses its own algorithms, for instance
to average things out. This may mean that some anomalies in fixing are
not obvious. As someone else said, you can always look at the
B-records in the IGC file itself, but this is better done through
analysis software designed to intepret them individually.

Ian Strachan
Chairman IGC GFA Committee

Hi All,

Yep, one of the b-records in my flight was corrupt, look at the log
time, shown with first 6 digits behind the B

in line 1 time is 21:12:32
in line 2 time is 22:36:00
in line 3 time is 21:12:40, look at the excerpt of Your IGC file below!

B2112323234199N10530479WA0334303580000022015000
B2236003402499N10530538WV0336003583000022015208
B2112403234260N10530608WA0338003602000020015000

The OLC did an administrative validation of my flight - THANK YOU OLC!

I received an e-mail suggesting to open the B-record in notepad, and
deleting the bogus line. Has anybody else tried this?

Chris 'CF'

You may have entered a time warp.

Had a similar experience a decade ago with my first (8-channel) GPS-20.
Over the Diamond Range during a flight out of Tonopah, the audio
vario changed to a theme from The Rocky Horror Show, and the GPS logged
me being back in 1946. Since I was in the middle of the Great Basin, I
didn't notice any change in the scenery during those 4 seconds.
Others thought it something to do with Area 51.
Jim

Tim, Ian,

Is the GPS data file sequence checking / analysis software you mention
in your separate posts available to us? If all FDRs screw up their data
files occasionally, it might be very useful to have such software more
generally available to soaring pilots.

-John


Tim Newport-Peace wrote:
'Out-if-Sequence' B-records are not exactly unknown. Some time ago a
wrote a simple program to sequence check .IGC file and catch these.
Cambridge is not the only manufacturer to suffer from this either.

Ian Strachan wrote:
By all means email the files (CAI and IGC) to me and I will look at
them with analysis software that enables every fix to be looked at in
detail. Some analysis software uses its own algorithms, for instance
to average things out. This may mean that some anomalies in fixing are
not obvious. As someone else said, you can always look at the
B-records in the IGC file itself, but this is better done through
analysis software designed to intepret them individually.

charlie foxtrot wrote:
Hi All,

Yep, one of the b-records in my flight was corrupt, look at the log
time, shown with first 6 digits behind the B

in line 1 time is 21:12:32
in line 2 time is 22:36:00
in line 3 time is 21:12:40, look at the excerpt of Your IGC file below!

B2112323234199N10530479WA0334303580000022015000
B2236003402499N10530538WV0336003583000022015208
B2112403234260N10530608WA0338003602000020015000

The OLC did an administrative validation of my flight - THANK YOU OLC!

I received an e-mail suggesting to open the B-record in notepad, and
deleting the bogus line. Has anybody else tried this?

Chris 'CF'

If you edit the B record, the OLC security check will indicate the file
was tampered with, which it was, and give you the dreaded red V. You're
not allowed to edit your flight logs. Thats the whole point of the
security check. The recorded position fix was "bad", but it was part of
the secure flight log in your *.cai file.

Your only option is to appeal to whoever is evaluating the log, the OLC
in this case, to ignore the obviously bad fix in the log.

-Dave
ZL

I received an e-mail suggesting to open the B-record in notepad, and
deleting the bogus line. Has anybody else tried this?

Chris 'CF'

If you edit the B record, the OLC security check will indicate the file
was tampered with, which it was, and give you the dreaded red V.

My experience is that this is not true. in the last 2 or 3 weeks I
erased a bogus line from a Cambridge 20 file, and it was then accepted
by the OLC with no red mark. Last year I did the same thing 2 or 3
times with no red mark, but maybe the security test was different then.


You're
not allowed to edit your flight logs. Thats the whole point of the
security check. The recorded position fix was "bad", but it was part of
the secure flight log in your *.cai file.

Your only option is to appeal to whoever is evaluating the log, the OLC
in this case, to ignore the obviously bad fix in the log.

-Dave
ZL