[OSM-newbies] Altitude/elevation with OSM and Josm

[Bernd Raichle]

On Saturday, 5 January 2008 10:19:14 +0100,
Harald Kirsch <pifpafpuf at gmx.de> writes:
 > Am 05.01.2008 10:02 schrieb Mark Williams:
 > > Harald Kirsch wrote:
 > >> Am 04.01.2008 23:31 schrieb Mark Williams:
 > 
 > >> Ok, thanks. Which brings me right to the next question. Is there a way
 > >> to convince JOSM to show altitute values form imported GPX tracks?
 > 
 > > It would be nice to have a plugin that looked for, say, the nearest 10 
 > > points & took a weighted average altitude - but you then have issues 
 > > around calibration (my Garmin can easily be 40metres out if the weather 
 > > changes). I'd love something you could activate for a session, which did 
 > > this for new nodes.
 > 
 > This sounds like you have a barometer in your GPS, which I have not.

No, it is easier to get a feeling for the altitude/elevation
variation:

(1) set the GPS receiver's logging mechanism to "every second", put it
    on the ground for a few minutes, and then look at the lat/lon/alt
    output; the differences of all logged points in lat/lon is lower
    than the alt differences.

(2) if you know the "exact" altitude/elevation for a point (e.g., a
    mountain's peak or a geodetical point with known altitude), you
    can see the absolute differences of the GPS signal and your used
    GPS receiver.


 > Nevertheless I get altitudes, and I would have thought they are not far
 > more off than the plane-coordinates, because GPS is "just"
 > triangulation. But from what you say I assume that the altitude
 > measurement provided by triangulation is even worse than the 40 metres
 > off. Is that true?

See other answers.

Currently I tag <ele> values for all points with a official known and
publicly given altitude.  For almost all mountain peaks there is a
altitude on a plate (or in wikipedia :-), and sometimes you can find
signs with an altitude on major foot paths etc.


Best wishes,
  -bernd