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Guest ba.roberts

elevation accuracy

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Guest ba.roberts

What sort of elevation accuracy would you expect to get with a handheld GPS receiver such as the Magellan GPS315? A friend and I (he has a Garmin) seem to get some strange results, but we are trying them in central London.

 

[This message has been edited by ba.roberts (edited 02-26-2001).]

 

[This message has been edited by ba.roberts (edited 02-26-2001).]

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Guest peter

Because of the basic geometry of the satellites you can see (i.e. none are below you), the vertical accuracy is worse than horizontal accuracy by about a factor of 1.5 - 2. So under ideal conditions, the altitude should be within about 15 - 20 m most of the time.

But conditions are rarely ideal, and in a city the only satellites you can see may be almost directly overhead which will degrade the accuracy. And if you can only see 3 satellites, the unit won't be able to determine the altitude at all.

BTW, older Garmin's (incl. the III+) seem to have a slight systematic error in the altitude calculation of about 10 m.

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Guest ba.roberts

Thanks Peter that's reassuring. We began to think we were going mad when it couldn't tell the difference between Ground Level and the the 8th floor.

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