4.1.14. How to Calculate Real Surface Area in QGIS

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  • เผยแพร่เมื่อ 17 ม.ค. 2025

ความคิดเห็น • 7

  • @JadeTimperman
    @JadeTimperman 2 หลายเดือนก่อน +1

    I tried to follow your steps, but I ran into some problems. I work with a DEM from ASTER with 30m resolution. When I use 'clip raster by mask layer', I do not get my shape file, it is rather a rectangle. However every pixel in that rectangle, that was not in my shape file, is set to zero, so it is kind of clipped. When I then proceed with 'Real Surface Area', the outcome is a raster with only the outlining of my shape file showing values, the inside is all put to zero. So when I get to zonal statistics, these give the exact same surface as my original uploaded shape file has. I work with Q-GIS version 3.32.3-Lima. Hope you can help me.

    • @JadeTimperman
      @JadeTimperman 2 หลายเดือนก่อน +1

      I could convert the entire DEM without clipping any, but this gave me something strange. As I have a raster with resolution 30m, this should give me a minimum value of each pixel of 0.09 hectares. However, the minimum value is 0, so I wonder how this is possible.

    • @georgiregrarians
      @georgiregrarians  2 หลายเดือนก่อน

      @@JadeTimperman Hey, the issue is probably one of two things - either there is No Data values in your dataset or the dataset is simply too low of a resolution for this particular work. If there are NoData values, you have to exclude them from the elevation banding by using the Transparency properties of the layer.

    • @JadeTimperman
      @JadeTimperman 2 หลายเดือนก่อน

      @@georgiregrarians Thank you for the quick answer! It turns out I had to reproject the DEM to a rectangular coordinate system to make it work.

    • @georgiregrarians
      @georgiregrarians  2 หลายเดือนก่อน

      @@JadeTimperman Oh yeah, good point. You can't have metric measurements if it's a geographic coordinate system. It has to be a projected one.

  • @vaso1512
    @vaso1512 7 หลายเดือนก่อน

    where can i find the "real surface area" algorithm?

    • @georgiregrarians
      @georgiregrarians  7 หลายเดือนก่อน

      You have to install the SAGA module