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Note: This is a one-time error that was observed over the course of approximately 10 minutes. The unit had been functioning correctly before and after this bug was observed.
Here are two parallel tracklogs from a 12xl sitting on the passenger seat and a fixed mount GPS-130 with GDR-21.
Please note that the two units show a difference of approx. 14826.17 meters (when comparing the 14:03:31 readings.) Note: this number is very close to the expected offset of 14826.86 meters that one would get if the 10485.76 meter correction was misinterpreted as a literal correction in both the X and Y directions, instead of the "don't use" pattern it is inteded to be. In fact, this observed error is only -0.69 meters off of that expected error.
The times listed are UTC-8 (PST). The differential ground station in use at the time was:
PIGEON POINT, CA
RBn Antenna Location: 37 11.2N, 122 23.4W
REFSTA Ant Location (A): 37 11.22466N, 122 23.39603W
REFSTA Ant Location (B): 37 11.20930N, 122 23.38588W
REFSTA RTCM SC-104 ID(A): 266
REFSTA RTCM SC-104 ID(B): 267
REFSTA FIRMWARE VERSION: RC00-1C19
Broadcast Site ID: 883
Transmission Frequency: 287 KHZ
Transmission Rate: 100 BPS
Signal Strength: 75uV at 180 NM
STATUS AS OF 31 MARCH 1997
Outages: Intermittent Off-air,
Scheduled Maintenance 1600Z 10Mar97 to 2359Z 15Mar97.
Off-air 0234Z 09Mar97 to 0745Z 09Mar97.
Off-air 1813Z 24Feb97 to 1230Z 25Feb97.
Off-air 1600Z 05Feb97 to 2200Z 05Feb97.
Track from 12xl:
Format: DDD UTC Offset: -8.00 hrs Datum[100]: WGS 84
T 03/20/1997 14:02:38 37.5515485 -121.9424004
T 03/20/1997 14:02:45 37.5512856 -121.9423736
T 03/20/1997 14:02:55 37.5507599 -121.9418854
T 03/20/1997 14:03:05 37.5500840 -121.9406302
T 03/20/1997 14:03:13 37.5497299 -121.9399382
T 03/20/1997 14:03:21 37.5494295 -121.9393481
****
T 03/20/1997 14:03:31 37.5486141 -121.9378675
****
T 03/20/1997 14:03:48 37.5470209 -121.9350297
T 03/20/1997 14:04:11 37.5448376 -121.9312156
T 03/20/1997 14:04:31 37.5429064 -121.9278360
T 03/20/1997 14:04:44 37.5417423 -121.9257654
T 03/20/1997 14:04:55 37.5411040 -121.9246335
T 03/20/1997 14:05:05 37.5409108 -121.9243706
T 03/20/1997 14:05:16 37.5401652 -121.9235284
T 03/20/1997 14:05:26 37.5396287 -121.9231904
T 03/20/1997 14:05:40 37.5384486 -121.9223858
T 03/20/1997 14:06:07 37.5356859 -121.9204170
T 03/20/1997 14:06:18 37.5344253 -121.9201971
T 03/20/1997 14:06:25 37.5339800 -121.9201864
T 03/20/1997 14:06:35 37.5339371 -121.9202615
T 03/20/1997 14:06:57 37.5336850 -121.9202829
T 03/20/1997 14:07:05 37.5328159 -121.9201113
T 03/20/1997 14:07:19 37.5311476 -121.9197358
T 03/20/1997 14:07:33 37.5292379 -121.9191349
T 03/20/1997 14:07:53 37.5261480 -121.9182176
T 03/20/1997 14:08:04 37.5245333 -121.9180084
T 03/20/1997 14:08:17 37.5225055 -121.9180674
From: GPS-130
Format: DDD UTC Offset: -8.00 hrs Datum[100]: WGS 84
T 03/20/1997 14:02:35 37.4829517 -122.0792073
T 03/20/1997 14:02:44 37.4824076 -122.0801146
T 03/20/1997 14:02:52 37.4816130 -122.0806356
T 03/20/1997 14:03:01 37.4807038 -122.0806535
T 03/20/1997 14:03:09 37.4798089 -122.0803751
T 03/20/1997 14:03:20 37.4790000 -122.0806804
T 03/20/1997 14:03:28 37.4780979 -122.0802763
****
T 03/20/1997 14:03:31 37.4777042 -122.0799978
****
T 03/20/1997 14:03:44 37.3834597 -122.0044704
T 03/20/1997 14:03:51 37.3831013 -122.0033835
T 03/20/1997 14:03:57 37.3827070 -122.0023505
T 03/20/1997 14:04:03 37.3823272 -122.0013265
T 03/20/1997 14:04:09 37.3819687 -122.0003473
T 03/20/1997 14:04:16 37.3815529 -121.9992065
T 03/20/1997 14:04:22 37.3811658 -121.9981825
T 03/20/1997 14:04:28 37.3807501 -121.9971225
T 03/20/1997 14:04:34 37.3803344 -121.9960355
T 03/20/1997 14:04:41 37.3799329 -121.9949756
T 03/20/1997 14:04:55 37.3797393 -121.9939605
T 03/20/1997 14:05:12 37.3794455 -121.9929634
T 03/20/1997 14:05:26 37.3789364 -121.9921101
T 03/20/1997 14:05:37 37.3782626 -121.9913645
T 03/20/1997 14:05:47 37.3775888 -121.9905650
T 03/20/1997 14:05:56 37.3768719 -121.9898733
T 03/20/1997 14:06:05 37.3761550 -121.9891727
T 03/20/1997 14:06:15 37.3753736 -121.9885439
T 03/20/1997 14:06:27 37.3746424 -121.9881217
T 03/20/1997 14:06:45 37.3752230 -121.9874031
T 03/20/1997 14:07:03 37.3750008 -121.9873312
T 03/20/1997 14:07:13 37.3741406 -121.9873222
T 03/20/1997 14:07:23 37.3732444 -121.9872234
T 03/20/1997 14:07:32 37.3723339 -121.9870169
T 03/20/1997 14:07:40 37.3714091 -121.9867833
T 03/20/1997 14:07:47 37.3705415 -121.9865138
T 03/20/1997 14:07:54 37.3696453 -121.9862533
T 03/20/1997 14:08:01 37.3687636 -121.9860287
T 03/20/1997 14:08:08 37.3679032 -121.9859120
T 03/20/1997 14:08:16 37.3669496 -121.9858670
T 03/20/1997 14:08:24 37.3660032 -121.9859120
(lat-lon-dist 37.4777042 -122.0799978
37.5486141 -121.9378675
)
14826.17 ; meters actual difference.
(* 10485.76 ; error in meters apparent for error signal
1.414 ; good old Pythagoras (2^0.5)
)
14826.86 ; meters expected.
(- 14826.17
14826.86)
-0.69 ; meters difference between expected and actual.
Note: once the differential radio was turned off and the RTCM corrections timed out in the GPS-130, the position returned to well within SA accuracies.
.
wolfgang.rupprecht+web@gmail.com
(Wolfgang S. Rupprecht)
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