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I'm trying to generate the hydrological analysis using processing and I have already done some terrain processing using the DEM.

In this moment, I'm working in he channel network but, when I assign in the elevation (the DEM) and in the Initiation Grid (the catchment area) the program gives me error.

Here are the screen shots of what has been generated:

this is the configuration in the channel network

this is the error

  • Fast forward to 2018 and QGIS 3 - this issue is still there and it cannot be bypassed even if all inputs have the same grid extent/CRS. Probably a bug? – Jakub Sisak GeoGraphics Apr 28 '18 at 13:55
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I've struggled with the same problem for a while. Even when they were in the same CRS the elevation and catchment grids were out by a couple of meters. I think it has something to do with the raster resolution and pixel size. I was able to get around this error by setting the pixel size to a round number (eg 5) when interpolation of the Elevation layer when interpolating to create the DEM.

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When I have seen that error it has often been because the coordinate systems do not match. Certain processing tools require input data sets to be in the same coordinate system to work properly, even if they otherwise appear to be correctly located onscreen.

That would be the first thing I check.

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Giacomo had it right: QGIS SAGA Channel network error: Input layers do not have the same grid extent Alter extent of one of the layers to the other (in QGIS save layer as)... and the tool works.

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Since Chanel network is a SAGA-GIS algorithm it is vital to get some knowledge on how this application is handling the data.

In SAGA's environment most of the grid calculations are being made within the one/same Grid System. The Grid System is SAGA's way of grouping loaded grids - in a simple words it groups adjacent grids. By adjacent you should understand grids that have:

  • the same cell size,
  • the same resolution (height px / width px),
  • the same spatial extent (basically the same x,y coordinates of most-western, most-southern corner).

So, in order to run this tool you need to pre-process your data - use some clipping and/or resampling tools in order to get a proper (same Grid System) input data for Chanel network algorithm.

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