Posts: 15
Joined: Mon Feb 19, 2018 9:09 am

Occasional incorrect processing of $FRCMD string

Fri Jun 08, 2018 3:14 pm


In my GPSGate set up, my Iridium trackers are sending data to a processing server, which decrypts and sends on to GPSGate server. This all works very well except that occasionally the $FRCMD string is not processed correctly by the GPSGate server. As as example, below are 3 successive commands sent to the GPSGate server at approx 2 minute intervals. I've highlighted the part that conveys altitude, speed and heading and also GPS time.


So the transmitted values are:
10:36:02 - 1800ft 109kn 187deg
10:38:03 - 2000ft 128kn 333deg
10:40:02 - 1600ft 18kn 189deg.

When the GPSGate server receives these, the one at 10:38:03 was processed incorrectly (incorrect values). Here is what GPSGate parsed:
gpsgate.JPG (25.31 KiB) Viewed 820 times

Or here's the export making it easier to illustrate the error:
track_data_id longitude latitude altitude ground_speed (M/S) heading utc_time_stamp valid
27 34.735333 -12.08285 1800 56.074402 187 2018-06-08T10:36:02 TRUE
28 34.735478 -12.083272 1800 0.618378 161.504064 2018-06-08T10:38:03 TRUE
29 34.735767 -12.084117 1600 9.26 189 2018-06-08T10:40:02 TRUE

Line 1 (track 27 at 10:36.02) shows 1800ft 56.07m/s (109kn) and 187 degrees (as sent in $FRCMD command)
Line 2 (track 28 at 10:38.03) shows 1800ft 0.618m/s (1.2kn) and 161.5 degrees (WRONG altitude, speed and heading!!!!!!!!)
Line 3 (track 29 at 10:40.02) shows 1600ft 9.26m/s (18kn) and 189 degrees (as sent in $FRCMD command)

Any idea why this is occasionally happening? (it's actually quite serious - this is tracking aircraft with event rules if speed is too low at altitude).


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