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I have digitized an LULC layer from satellite imagery, now I want to extract the elevation data from it. I have obtained DEM images from SRTM amd ASTER. How do I proceed?

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    Perhaps you can say what tools you have available? – BradHards Dec 13 '14 at 8:57
  • Or another way of putting BradHards comment, what software, version, license level, and/or extensions are you working with? And further, LU/LC polygons are going to be quite large and could have a fairly wide elevation range throughout. Is there a particular way of determining the elevation you'd want to use? Ie mean, greatest, least, etc. What do you intend to do with the result? It might make more sense to leave elevation off the attributes of your LU/LC polygons and use the information in a different manner depending on your analysis goals. – Chris W Dec 13 '14 at 18:54
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If you happen to use QGIS, install the Raster Interpolation plugin, which lets you to extract DEM elevation data and assign it to point layers.

Since I think you deal with polygons, you could first generate centroids* (or a representative point for each polygon) for those polygons and use the points to pick elevation data from the DEM.

Finally, join your polygon and point layer and copy the elevation data to your polygon layer.

Not sure if that's the best way to get it done, though. I didn't actually try it, but if you are lost on any step, tell me and I'll elaborate a bit more on that.

  • Be aware that in some cases a centroid could lay outside of the base polygon, other algorithms ensure points lay inside polygons. I'd use the ST_PointOnSurface function from PostGIS.

On the other hand, if you actually need Z coordinates assigned to each vertex of your polygons, then that could be a good idea for a QGIS plugin.

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