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I have a uBlox LEA-6H gps as an external GPS for an APM 2.0. I get great locks and the GPS coordinates are approximately correct, but the output is strange. I have a custom datalog routine to save all the gps data.

It starts out ok:

Timestamp (milliseconds) GPS time (hhmmss.sss * 1000 in UTC) GPS Status (0 = No Lock, 1 = Lock) Number of satellites acquired Latitude (degrees) Longitude (degrees) Altitude (meters) Altitude via GPS along (meters) Ground speed (m/s) Ground course (degrees)

GPS: 104316, 408893600, 1, 9, 43.7914470, -110.9391300, 2820.4900, 2843.4199, 7.4800, 257.4300
GPS: 104417, 408893800, 1, 9, 43.7914470, -110.9391300, 2820.1599, 2843.0601, 7.3400, 244.6900
GPS: 104517, 408893800, 1, 8, 43.7914390, -110.9391300, 2819.8999, 2843.0601, 7.3400, 244.6900
GPS: 104617, 408894000, 1, 8, 43.7914390, -110.9391300, 2819.6101, 2842.5701, 7.3400, 244.6900
GPS: 104718, 408894000, 1, 8, 43.7914390, -110.9391300, 2819.3101, 2842.5701, 7.3400, 244.6900
GPS: 104818, 408894200, 1, 8, 43.7914390, -110.9391300, 2819.1101, 2842.2100, 5.7100, 232.0800
GPS: 104919, 408894200, 1, 8, 43.7914280, -110.9391600, 2819.1101, 2842.2100, 5.7100, 232.0800
GPS: 105018, 408894400, 1, 8, 43.7914280, -110.9391600, 2819.3000, 2841.7700, 7.4700, 236.5400
GPS: 105118, 408894400, 1, 8, 43.7914160, -110.9391700, 2819.0400, 2841.7700, 7.4700, 236.5400
GPS: 105219, 408894600, 1, 8, 43.7914160, -110.9391700, 2818.8301, 2841.3501, 7.3900, 247.6500

(columns 5 and 6 are Lat and Long; column 2 is GPS time (hhmmss.sss * 1000 in UTC); column 1 is ardupilot milliseconds since startup.)

However, after a while I get both the GPS time and the longitude locking up:

GPS: 311568, 409027000, 1, 8, 43.7951700, -110.9478400, 2418.8999, 2607.6599, 5.3400, 327.8600
GPS: 311668, 409027000, 1, 8, 43.7951700, -110.9478400, 2418.3301, 2607.6599, 5.3400, 327.8600
GPS: 311768, 409027000, 1, 8, 43.7951700, -110.9478400, 2418.0300, 2607.6599, 5.3400, 327.8600
GPS: 311868, 409027000, 1, 8, 43.7951810, -110.9478400, 2417.6499, 2607.6599, 5.3400, 327.8600
GPS: 312049, 409027000, 1, 8, 43.7951810, -110.9478400, 2418.4600, 2607.6599, 5.3400, 327.8600
GPS: 312148, 409027000, 1, 8, 43.7951890, -110.9478400, 2418.8201, 2607.6599, 5.3400, 327.8600
GPS: 312249, 409027000, 1, 8, 43.7951890, -110.9478400, 2419.1399, 2607.6599, 5.3400, 327.8600
GPS: 312349, 409027000, 1, 8, 43.7952000, -110.9478500, 2420.0200, 2607.6599, 5.3400, 327.8600
GPS: 312450, 409027000, 1, 8, 43.7952000, -110.9478500, 2420.3701, 2607.6599, 5.3400, 327.8600
GPS: 312550, 409027000, 1, 8, 43.7952080, -110.9478500, 2420.8401, 2607.6599, 5.3400, 327.8600
GPS: 312650, 409027000, 1, 8, 43.7952080, -110.9478500, 2420.8401, 2607.6599, 5.3400, 327.8600
GPS: 312751, 409027000, 1, 8, 43.7952160, -110.9478700, 2420.5100, 2607.6599, 5.3400, 327.8600
GPS: 312851, 409027000, 1, 8, 43.7952160, -110.9478700, 2420.3501, 2607.6599, 5.3400, 327.8600
GPS: 312950, 409027000, 1, 8, 43.7952270, -110.9478700, 2419.9199, 2607.6599, 5.3400, 327.8600
GPS: 313052, 409027000, 1, 8, 43.7952270, -110.9478700, 2419.6799, 2607.6599, 5.3400, 327.8600
GPS: 313151, 409027000, 1, 8, 43.7952310, -110.9478800, 2419.1001, 2607.6599, 5.3400, 327.8600
GPS: 313332, 409027000, 1, 8, 43.7952310, -110.9478800, 2418.3899, 2607.6599, 5.3400, 327.8600
GPS: 313432, 409027000, 1, 8, 43.7952420, -110.9478900, 2417.8799, 2607.6599, 5.3400, 327.8600 

And then there is a weird jump (this is contiguous with the previous text in the log file). Note how the longitude has a big jump right after the GPS time suddenly starts responding. The Ardupilot milliseconds has no jump in time (goes from 313432 to 313532, which is 10hz).

GPS: 313532, 409102600, 1, 8, 43.7952420, -110.9478900, 2417.3201, 2472.6299, 5.6800, 278.6700
GPS: 313632, 409102600, 1, 8, 43.7940290, -110.9520800, 2416.9500, 2472.6299, 5.6800, 278.6700
GPS: 313733, 409102800, 1, 8, 43.7940290, -110.9520800, 2416.7100, 2472.3799, 5.0400, 277.8500
GPS: 313833, 409102800, 1, 8, 43.7940290, -110.9520900, 2416.4199, 2472.3799, 5.0400, 277.8500
GPS: 313933, 409103000, 1, 8, 43.7940290, -110.9520900, 2416.1399, 2472.2700, 5.1700, 274.8200
GPS: 314034, 409103000, 1, 8, 43.7940290, -110.9521000, 2416.0601, 2472.2700, 5.1700, 274.8200
GPS: 314134, 409103200, 1, 8, 43.7940290, -110.9521000, 2416.0400, 2472.2800, 3.8500, 269.5900
GPS: 314234, 409103200, 1, 8, 43.7940290, -110.9521200, 2416.0400, 2472.2800, 3.8500, 269.5900
GPS: 314334, 409103400, 1, 8, 43.7940290, -110.9521200, 2416.0801, 2472.2200, 3.3400, 261.7400
GPS: 314434, 409103400, 1, 8, 43.7940290, -110.9521300, 2415.9600, 2472.2200, 3.3400, 261.7400
GPS: 314534, 409103600, 1, 8, 43.7940290, -110.9521300, 2416.1001, 2472.2400, 3.7000, 251.8900
GPS: 314635, 409103600, 1, 8, 43.7940250, -110.9521400, 2416.1201, 2472.2400, 3.7000, 251.8900
GPS: 314735, 409103800, 1, 8, 43.7940250, -110.9521400, 2416.1899, 2472.1599, 3.0700, 244.8900

The GPS coordinates are approximately in the right location according to google earth, but it is not exactly in the correct location.

What could be causing these errors?

I can post the full log file and kml file if it would help.

Thanks,

Tom