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I am using a Digital Surface Model with 1m-resolution to perform a visibility analysis. The laser obviously also hit the power cables which cross the area, so these elevated points now act as a "wall" through the landscape which casts visibility "shadows" which in reality do not exit.

I am looking for the right procedure to filter those extreme values from the elevation data, but also keep the real obstacle like the tree in the image, which is crossed by the cables. enter image description here

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  • The simple stuff first. Can you set a height threshold, or are some trees taller than your power lines?
    – GeoMonkey
    Commented Dec 8, 2022 at 15:08
  • @GeoMonkey sorry for being to late to my own party. The cables are , i think, minimum 20 meters higher that other things. Of course they have no exact height, cause they have their maximum at the posts which are like 50 meters and and then hang down and rise to the next post.
    – Bernd V.
    Commented Dec 13, 2022 at 18:00
  • In that case, if your power cables are much taller than everything else, then just filter out values based on a max value. For example, if your power cables are 20m and your tallest tree is 15m, then just set all values above 15m to 0m (or nan). Does that make sense?
    – GeoMonkey
    Commented Dec 13, 2022 at 21:34
  • @GeoMonkey errm, and how would I do that exactly? Which tool will do it? I'm pretty much lost when searching for "filter" in QGIS
    – Bernd V.
    Commented Dec 14, 2022 at 15:25
  • ah okay, you can use a tool called raster calculator. In Qgis 3.2.2 onwards this now supports an 'if' statement. Generally if statements work like if(x>20, 0, x). This basically says "where x (your image) is greater than 20, give it a value of 0, else give it the value of the image". Some info that may be helpful is here: gis.stackexchange.com/questions/385763/…
    – GeoMonkey
    Commented Dec 14, 2022 at 17:05

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