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Old 12-29-2007, 11:19 PM   #114
TomW
Beastly Adventurer
 
Joined: Jan 2006
Location: Ft. Payne, AL
Oddometer: 1,013
Quote:
Originally Posted by SpotMaker
I'd like it if you could elaborate on the points you believe to be 10 miles off. We have recorded literally MILLIONS of fixes with the GPS chipset in SPoT units. The worst error we've ever seen is around 100 yards, and that's under abysmal signal conditions with a 2D GPS fix.

A 10 mile error (or even a one mile error) is essentially contrary to certain laws of physics.

Since the check in message that is successfully received might be the third attempt, and that third message may be sent up to 20 minutes after the GPS fix was obtained, you would only have to be traveling 30 MPH to have moved 10 miles between the time the GPS reading was taken and the message successfully got through. Is is possible that this was the case?
I agree that it sounds unlikely; however....

Re: your last comment, I was in tracking mode; therefore, the location would only be sent once. Actually, the location that was 10 miles off was sent when I was parked. The next SPOT tracking message sent from the exact same location was correct. I can send you the SPOT message log if you'd like.

Comparing times with the Garmin's track log, the other spurious SPOT locaton was a little over 4 miles off, not 1 mile as I originally thought. As a control, I checked a couple other locations and the SPOT and Garmin locations are dead on with a few seconds SPOT lag time applied to the points when I was in motion. I've plotted up the anomalous locations and paired them with the Garmin GPS location from the same time. The Garmin locations are recorded every few seconds and plot on the map as a true record of where I was. The image file is a bit big, so I'll PM it to you.

All GPSs I've had will occasionally throw out a weird location -- that's why the max speed on the things sometimes reads 542 mph, and, sure enough, when I go back through the track log, there's a flyer in there. I'm curious to learn what the issue is here.

Cheers.
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TomW
'76 R90/6
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'99 XR100
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