Again on altitude issues

[Mike11]

Hello,



as I've said in this thread (http://www.oruxmaps.com/foro/viewtopic.php?f=3&t=3009&p=9767#p9767">http://www.oruxmaps.com/foro/viewtopic. ... 9767#p9767">http://www.oruxmaps.com/foro/viewtopic.php?f=3&t=3009&p=9767#p9767) I'm experiencing constantly height jumps in my tracks.



I just want to know a couple of things:



1) How I can correct this problem?



2) The GPS track is correct in terms of latitude and longitude and I'm using DEM file to get the altitude of the point. So I if understand correctly once I have the right GPS point in terms of latitude and longitude (and I have that) the software should ask the DEM file what is the altitude of that point, right? So how is possible that I have some points with -8000 meters of altitude?



Thanks,

Mike

[nurembergueso]

1) How I can correct this problem?



2) The GPS track is correct in terms of latitude and longitude and I'm using DEM file to get the altitude of the point. So I if understand correctly once I have the right GPS point in terms of latitude and longitude (and I have that) the software should ask the DEM file what is the altitude of that point, right? So how is possible that I have some points with -8000 meters of altitude?

• Probably not at all, except by deleting these points afterwards. Especially in the mountains with narrow valleys and steep hillsides GPS accuracy is insecure and measuring errors are common. Therefore some recommend to use a barometer as Altimeter instead.
 

• I expect the DEM files cover the region you are on your way (otherwise the altitude would be -9999 m). Then there's still the question, how precise is the DEM data?
  

In other words, is there really for each one arc second square you are located to an corresponding altitude value? (Which btw is rather imprecise again. A position 30 m more or less beside the path in a gorge can locate you to its bottom or hundreds of meters above.)

From a walk in the Polish Carpathian I know there are some "black holes" in DEM files and if you have a look at http://viewfinderpanoramas.org/dem3.html#hgt[/url] under Alps you'll see there might be some in the Italian Alps, too.

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