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I'm looking for GIS program that has good support for KML/KMZ or GPX route files and also has free hand selection tool. Right now I use 3dem and it would be perfect for my needs if only it had that free hand selection tool. All I need is to load a terrain (HGT file), and then select only the part of it that is close to my route plan (KML file). And finally save that selected part to DEM file or any other format that I could edit later in some 3D modeler.

I'd appreciate it very much if someone could point me to some GIS program that fully meets my requirements.

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up vote 5 down vote accepted

You should be able to do this task in a variety of GIS applications. Here's a step-by-step for QGIS.

  • Download QGIS from: http://www.qgis.org/
  • Import the KML or GPX polyline (Layer > Add vector layer...).
  • Import the elevation data (Layer > Add raster layer...)
  • Either: create a buffer area around the polyline (Vector > Geoprocessing tools > Buffer(s))
  • Or: manually define the area to clip by creating a new polygon shapefile (Layer > New > New Shapefile Layer...)
  • Clip the elevation data to the buffered area (Raster > Extraction > Clipper)

If your track spans multiple HGT tiles you'll need to mosaic them. You can do this with a virtual raster catalog (Raster > Miscellaneous > Build Virtual Raster (Catalog).

Note that if you buffer the polyline without reprojecting the SRTM elevation data (which comes in WGS84) the units of distance will be in decimal degrees, not meters. You can reproject the data by going to Raster > Projections > Warp (Reproject).

example

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Thank you very much for your reply and all instructions. I already followed first 3 steps and now got stuck on 4th one. Here's the view of my track and HGT file: [IMG]i44.tinypic.com/20aqbev.png[/IMG] –  Grigory May 1 '13 at 19:53
    
Oh, gosh... I cannot edit my post above so I'll continue here. Could you tell me please what options and values should I choose from this Buffers menu so I would have result similar to the one you posted? And second question, regarding the reprojecting of SRTM file - what system I need to choose as output one so I could have distance in meters? –  Grigory May 1 '13 at 20:04
    
The projection will depend on your location. Either use a national projection (in my example I used the British National Grid EPSG:27700, as the tile was in England) or an appropriate UTM projection. In my example I used a 2000m buffer. –  Snorfalorpagus May 1 '13 at 21:17
    
I have a question - how can I change projection of my KML file? I managed to change projection of HGT file but cannot change it for KML. –  Grigory May 2 '13 at 19:10
    
KML always uses WGS84 projection. Try converting it to an ESRI Shapefile. –  Snorfalorpagus May 2 '13 at 22:19
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