On 30/01/2013 21:33, Sebastian Arcus 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.
Just about any GPS device can use the GPS satellites to get the
elevation. With modern GPS devices with high sensitivity receivers, this
is usually pretty accurate.
The barometric altimeter is supposed make the elevation more accurate.
It may help a bit if you have poor GPS reception, eg under trees, or in
a canyon or between tall buildings. But the altimeter can be affected by
changes in air pressure or weather. Its debatable as to whether it
actually helps much.
For a compass, if you are moving then the device can figure out your
direction from the GPS satellites. But this doesn't work if you are
stopped. So a compass is handy if you walk up to a junction, then stop
and check which way your GPS is pointing.
Though even without a compass, you don't have to move very far for the
GPS to point the right way, about a metre or so should do. So you can
probably manage without this (unless you are trying to navigate at the
top of a cliff).
So the altimeter and compass don't really matter for OSM mapping.
Elevation data is not usually added to OSM, so it doesn't matter whether
or not your GPS tracks contain accurate elevation data. And the compass
direction is not recorded in the track anyway.
Personally, I would say just get the Etrex 20, as it is a bit cheaper.
Craig
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