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I have a series of building polygons which I would like to convert to a raster illustrating their height. I have the building heights but not their elevation above sea level datum. I have the underlying topographical data in a DEM. So, I was wondering if someone could show me an algorithm in the Field Calculator that will allow me to combine the two to arrive at a building elevation above sea level.

(Apologies if this is an easy question, I am a newbie to GIS, or has been asked before but I couldn't find it in the previous questions)

Yours in hope

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    I just noticed you got the same answer to your previous question gis.stackexchange.com/questions/123695/…. Could you clarify what your problem is? – underdark Nov 27 '14 at 21:09
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    The problem is my lack of knowledge of QGIS. I am trying to work out how to add buildings and woodland to a DEM so that I can run a ZTV in Grass. I tried the solution suggested in the other question but it didn't seem to work so I thought I must be doing something wrong. Thus, I wanted to check if I wasn't missing a step that the other guys would have assumed I knew. I guess the beauty of being ignorant is that everything is new and exciting! – joverall Nov 27 '14 at 22:51
  • The only issue I can think of is CRS, see my edit. – underdark Nov 28 '14 at 18:29
  • It was the very useful question for me! Thank you so much!! and @underdark, too – cmcromance Dec 28 '16 at 6:07
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That's a two step process

  1. rasterize the building layer to create a raster with the building height information
  2. use field calculator to sum up the DEM and building height

Note that the two rasters have to be in the same CRS before you can add them up in the field calculator.

  • Thanks for the answer UD. Will this process allow me to create a new DEM that includes the building height information above the existing ground level? – joverall Nov 27 '14 at 21:11
  • Yes, the resulting raster layer will be the sum of DEM height plus building height. – underdark Nov 27 '14 at 21:13

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