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We have excavated a very large 5.000 year old fish fence, which was documented by photogrammetry, and is now being digitized. I started digitizing the orthophoto in QGIS and everything is cool. Now I've been ask to add Z-values to each of the corresponding polygons (pieces of wood). I then created a DEM of the model in Agisoft Photoscan Pro, and all the information is there.

Is there a way to to automatically transfer the Z-values from the DEM, to the overlaying polygon?

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I guess that your fish fence polygon covers several DEM grid cells. Normally you would extract DEM grid values to a point layer with a plugin tool like Point sampling tool. If you polygons are very small in relation to the DEM cells you could use the centroid of the polygon as a new point layer doing the Point sampling plugin tool on that point layer.

With another QGIS plugin - Zonal Statistics you can calculate the sum, the mean value and the total count of the pixels, that are within a polygon. https://docs.qgis.org/2.2/en/docs/user_manual/plugins/plugins_zonal_statistics.html

  • cheers! I shall test it asap. – Theis Jensen Apr 29 '15 at 11:50
  • It worked! Thanks a lot! Hooorah! I just had to add a point to each of the polygons, and then use the point sampling plugin. – Theis Jensen Apr 29 '15 at 12:49

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