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In order to calculate TWI, I had to generate a catchment area raster, but I don't understand what the values of pixel represent. Any clarification?

The DEM is projeted in EPSG : 2154, so the unit is meter

I used the SAGA 'catchment area' tool

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  • Namoat- I think we need some more information. What was your process? Specifically what tools did you use? And what units was your DEM in?
    – Baswein
    Jun 14 '20 at 13:55
  • @Baswein The DEM is projeted in EPSG : 2154, so the unit is meter. I used the SAGA 'catchment area' tool
    – Namoat
    Jun 14 '20 at 14:16
  • I usually use flow accumulation which is the number of upstream pixels. I assume Catchment area is the area of upstream pixels but can not confirm. One way to confirm that is to run the channel network and drainage basins saga algo. However looking at your screenshot it appears that you did not fill the sinks in your DEM before running the algo which will give you wrong and confusing results.
    – Baswein
    Jun 14 '20 at 15:10
  • @Baswein okey thanks a lot. for the sinks filling, I did not , do you know where I can find all the steps to follow, from DEM to TWI ? I can't find a clear method . Thanks again
    – Namoat
    Jun 14 '20 at 15:26
  • Hans van der Kwast is usually really good. I haven't followed this one youtube.com/watch?v=aHCLCUwg3O0
    – Baswein
    Jun 14 '20 at 15:31

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