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Author Topic: Altitude problem  (Read 1179 times)

brad

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Altitude problem
« on: January 24, 2012, 03:57:25 am »

Hey, just wondering if anyone knows why my watch is giving me some weird altitude values, i am on the water most of the time with the exception of coming in for a break on the beach but the graph when i come in gives me values usually from 3-12m high, shouldn't it be 0 or 1m most of the time?


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« Last Edit: January 24, 2012, 04:00:19 am by brad »
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gerhard

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Re: Altitude problem
« Reply #1 on: January 24, 2012, 03:30:32 pm »

i am on the water most of the time with the exception of coming in for a break on the beach but the graph when i come in gives me values usually from 3-12m high, shouldn't it be 0 or 1m most of the time?

Its GPS accuracy limitation. The graph actually looks very good compared to other devices.
The GPS median error is maybe 3m at the best like on the sea for the 625XT (slightly better than older products). The average is higher than that. You do not notice the error so much. The back forward error causes some fluctuating speed, right-left some wiggling and a distance error.

For elevation, the distance error is up to twice the distance errors (you would need sats on the other side of earth to get better accuracy). So 12m is quite good. (Actually, the device should filter the raw values, the read values are higher.)

Solution? Use elevation correction, getting the elevation from a database instead. Not so good on bridges and in canyons, but gives a better profile. Available in for instance SportTracks (as a plugin).
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