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I have run a viewshed analysis on a single point using a UK OS Terrain 5 DTM which has worked fine. I now need to perform the same analysis but with buildings and woodlands taken into account.

I've have OS Vectormap District data for both the buildings and the woodland areas which are shape files and want to add generic height values to each of these. Am I right in thinking that this is the process?

  • Add 'Height' attribute field of 5 to buildings and 15 woodland layers (Conservative values)
  • Convert both polygon layers to rasters
  • Use the raster calculator to add the two new rasters to the existing DTM (I'm not familiar with this so a step by step process would be very useful). When running this it's masking out the areas that are not woodland or buildings (presumably NoData areas). How do you assign a value of 0 to these NoData areas?
  • Run viewshed again using new DTM

One final question - how can I avoid the viewshed calculating 'on top' of those features? (i.e. the woodland and the buildings)

  • What happened when you tried this? – PolyGeo May 4 '17 at 20:28
  • I've converted both polygon layers to rasters but ran into issues with the raster calculator. Firstly it was failing altogether which turned out to be that it didn't like the characters I was using in the output name. Secondly the calculator was working but was removing the rest of the DTM. Another search in other questions like this suggested that you should 'Make sure that the background cells in the output raster (cells where there are no trees) are assigned a value of zero rather than NODATA.' I can't figure out how to do this though. – Stirling May 5 '17 at 8:08
  • Please use the edit button to revise your question with this and any other requested clarifications. – PolyGeo May 5 '17 at 8:35

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