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I would like to calculate the true surface area of a region from DEM (2D elevation data).

Is it possible to do this with QGIS?

And if yes, how?

I managed to obtain a 3D visualization of the elevation data using nviz (a GRASS-module) but I do not see any possibility to calculate the 3D surface area.

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Yes, it's possible. The GRASS module is r.surf.area. You can use OPEN GRASS Tools (GRASS plugin of QGIS). Its use is very intuitive. For irregular surfaces you have to use a mask.

1) Using the module in the square area (red) of next image:

enter image description here

2) Results in Output Window:

enter image description here

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  • Thank you very much for your quick reply! I tried to use it, however if I clicked on a red square tool nothing happened. So I was not able to select the region of interest as you showed it in a picture. I got the output but it is difficult to interprete since the area of interest was not selected.
    – Olga Fishkis
    Commented Mar 24, 2015 at 16:45
  • Sorry, I thought that you were familiar with GRASS plugin of QGIS. In OPEN GRASS Tools, the last icon is for editting current GRASS region. In this way, I selected the rectangular red edge area for calculating 3D area in my huge dem raster (icon below the hammer is for visualizing or no this region). However, you can use a mask for irregular areas. After, I ran the module with a simple click in Run.
    – xunilk
    Commented Mar 24, 2015 at 17:43
  • Thank you so much! That was really a great help. I could measure it now.
    – Olga Fishkis
    Commented Mar 25, 2015 at 7:32
  • What if the area to calculate is not a rectangle but an irregular shape. Is there a way to use a 2D polygon as a mask?
    – A_NeriWinter
    Commented Jan 16, 2018 at 15:59
  • @AN For yesterday Yes, there is. You can use a 2D polygon as a mask outside GRASS (QGIS Processing Toolbox; clip raster by mask layer) and, afterward, load it in its respective GRASS Mapset of QGIS.
    – xunilk
    Commented Jan 17, 2018 at 17:24

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