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Occasional Problem With GPS -- Anyone Else?


MysteryGuy1

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I have a Garmin Etrex that, for the most part, has served me well. But once in a while, the purple line showing the direction of the cache takes an unusually long time to adjust after I've changed course. For example, it might show that the cache is due left, so I turn left and start walking, but the purple line continues to point due left for a lot longer than I'd expect. The distance to the cache, however, continues to count down properly. Anyone else experience this?

Edited by MysteryGuy1
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Most etrex's don't have a real compass in them, they determine direction by your recent movements. Slow, short movements aren't enough to determine this.

 

Distance is easy to determine with GPS, direction however, has never been part of how GPS works.

 

Actually, that's not true, though it is a commonly-held misconception. GPS measures motion not by comparing recent fixes, but by Doppler measurements of the satellite signals. Every GPS measurement includes a velocity (speed and direction) fix as well. Both speed and direction are very accurate.

 

The issue here is that the Etrex may well be programmed to ignore speeds below some certain threshold or for a certain amount of time. That's because the very act of swinging your arm when walking could cause the GPS arrow to do wild gyrations if it weren't damped in software.

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I sometimes suffer something similar on a Garmain Dakota 10 - although it is fairly infrequent.

 

The numbers count down but there's no direction change.

 

Thinking back to occasions where it has happened, often it is on the final approach to a cache, at the point where my speed is likely to be lower - but definitely not always.

 

The Dakota 10 also does not include a magnetic compass.

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