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Altitude dodgy?

 
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peat
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Joined: Nov 01, 2004
Posts: 18

PostPosted: Mon Nov 01, 2004 9:09 pm    Post subject: Altitude dodgy? Reply with quote

Hello,

I recently got my Holux Gr 230 and have been testing it out with
Memory map 2004 and my Ipaq 3970.

Everything is going well apart from the altitude is way out.
On the map it is saying 17ft height but on my recorded track from the gps it is saying 185ft at the same position.
I was getting a good gps signal with 7-8 satellites at the time so it isnt a poor signal.
Does anyone know whats going on?
Thanks
Pete.
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Skippy
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Joined: 24/06/2003 00:22:12
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Location: Escaped to the Antipodies! 36.83°S 174.75°E

PostPosted: Mon Nov 01, 2004 10:22 pm    Post subject: Re: Altitude dodgy? Reply with quote

peat wrote:
Does anyone know whats going on?


Welcome! Thumbs Up

Basically, the world is not round and the mean sea level varies by several hundred feet, depending on your location.

The data returned from the GPS gives your altitude and a correction factor. I would guess that what has happened is that Memory Map is applying the altitude correction information to get the true height above mean sea level but the track log is showing you the uncorrected height. A very detailed explanation can be found here:

http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=10915

The other thing to remember that the accuracy of the altitude reported by your GPS is roughly half as accurate as your location. So if the location accuracy is ~30ft then the height may be off by ~60ft.
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peat
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Joined: Nov 01, 2004
Posts: 18

PostPosted: Wed Nov 03, 2004 12:50 am    Post subject: Reply with quote

Ah thanks.

So basically, ignore the altitude readings Smile

ta
Pete.
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