[OSM-newbies] Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

[John F. Eldredge]

Sebastian Arcus <shop at open-t.co.uk> wrote:

> I was looking at the eTrex series from Garmin to use for mapping on
> OSM, 
> as they seem to be robust, compact and have specially long battery
> life 
> (25 hours on 2 AA batteries). The main difference between 20 and 30 
> seems to be that 30 has altimeter and compass, while 20 doesn't have 
> them. Is this important when recording GPS tracks to use for mapping
> on 
> OSM? Doesn't compass and altitude data come from GPS satellites
> anyway? 
> Or an internal altimeter and compass are more accurate?
> 
> If anybody here has either of the above GPS units and uses them for 
> mapping, it would be useful to hear a first hand opinion.
> 
> Thanks,
> 
> Sebastian
> 
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The altitude reading on civilian-model GPS units is not particularly reliable; the altitude information from the satellites has deliberate random errors built in, to make it difficult for someone to use a civilian GPS to plan an artillery or rocket attack.  The GPS units used by the US military can decode more accurate, but encrypted, altitude data.

-- 
John F. Eldredge -- john at jfeldredge.com
"Reserve your right to think, for even to think wrongly is better than not to think at all." -- Hypatia of Alexandria