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I am using QGIS 2.18.19 to produce viewsheds of a proposed development to show where the development would in theory be visible from. I am using Ordnance Survey Terrain 5 as my height data (*.asc) which I have loaded and saved out as a GeoTIFF so that it is correctly geo-referenced to the coordinate reference system I am using (OSGB36).

At present I have run a viewshed of the development using the DTM which gives the theoretical visibility as if the earth was bare. I have a separate vector dataset of woodland which I have converted to a raster.

Firstly, how can I add give the woodland raster a notional height so that each block of woodland has a height of 10m?

Secondly, how do I add the raster of the woodland (with notional woodland height) to the DTM so that I have a raster of the DTM with woodland heights?

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  • Not a duplicate, but it basically works like this: gis.stackexchange.com/a/307648/107424. Just use your woodlands polygon instead.
    – MrXsquared
    Feb 8, 2019 at 15:30
  • Thanks - followed that tutorial through trying it using Raster - Conversion - Polygon to Raster and also using Rasterize (Vector to Raster) via processing toolbox and the Raster conversion way worked perfectly!!
    – DavidG
    Feb 8, 2019 at 16:50
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    @DavidG If you write that up as an answer to your own question it will help other people who come to this site.
    – csk
    Feb 8, 2019 at 17:42
  • Just a thought but have you had a look at what DTMs and DSMs if any are available from the EA for your area of interest? The DTMs are bare-earth models and the DSMs include surface vegetation and buildings. See: ckan.publishing.service.gov.uk/publisher/… and ckan.publishing.service.gov.uk/publisher/…
    – nhopton
    Feb 10, 2019 at 9:27
  • Thanks - yes I have looked at the EA's DSMs although coverage is patchy in my area of interest
    – DavidG
    Feb 14, 2019 at 16:40

1 Answer 1

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As already said in comments, the question is different, but the solution is very similar to the one provided here.

  1. Add a height attribute to your woodlands vector layer.

enter image description here

  1. Convert your woodlands layer to raster. (Using SAGA Rasterize tool here as the QGIS2 tool is.. well, lets say outdated). Make sure to choose your heightattribute as Attribute and set the cellsize to your original DEMs cellsize.

enter image description here

  1. Run r.null on your just rasterized layer to replace null values with 0.

enter image description here

  1. Use Raster Calculator to add the height to your original DEM. Use "OriginalDEM@1" + "NullRaster@1"

enter image description here

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  • That's the process I followed. The only slight difference was I did not need to use r.null to remove null values
    – DavidG
    Mar 14, 2019 at 13:25
  • @DavidG, consider accepting (and or upvoting it) the answer if it solved your Q. See: gis.stackexchange.com/help/someone-answers. Tks.
    – Andre Silva
    Mar 17, 2019 at 2:25

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