[QGIS-Developer] Slow WCS processing and Clipping WCS by extent not working

[Raymond Nijssen]

Created an issue too:
https://github.com/qgis/QGIS/issues/67061


On 8/14/26 07:02, Raymond Nijssen via QGIS-Developer wrote:
> Dear developers,
> 
> Currently I'm working on a process that uses a WCS service containing 
> elevation data. I need 800x800m pieces from the elevation raster.
> 
> My graphical model uses a Raster Calculator algorithm, with one of the 
> (2) layers being the WCS layer from my project. This works but is very 
> slow. It takes about 1 minute to process the 800x800m calculation.
> 
> If I download the raster using gdal_translate, it only takes 2 seconds 
> or so. I cannot find out what the Raster Calculator is doing differently.
> 
> On top of that, I need to do calculations for the same area 3x, so every 
> location takes up over 3 minutes, and my entire process with many 
> locations over 6 hours.
> 
> So I had some ideas to speed this up, but so far they all have downsides 
> and I'm not sure what is the best way to proceed:
> 
> 1. Using the Raster Calculator with only one layer and storing the 
> output for the next 3 calculations. Will still take 1 minute extra, but 
> is more effective (and a bit lame).
> 
> 2. Using the Clip Raster by Extent algorithm, which seems perfect for 
> this. But it does not work for WCS, cause it parses the QGIS layer 
> source string directly into gdal_translate but GDAL needs another string 
> and throws an error. Looking at the Python source code, this has 
> probably never worked for WCS.
> 
>    2a. Fixing the Clip Raster by Extent algorithm. Cause it is in 
> Python, I can give it a try. But I already found out that the Clip 
> Raster by Mask algorithm has the same issue. And maybe more raster 
> algorithms do. So that should be solved in less redundant way, right?
> 
>    2b. Asking a core developer to rewrite this properly in c++. Maybe in 
> a way that uses the QGIS network manager so the http-calls get shown in 
> the debugging panel? No idea what this would cost but I think I can get 
> this funded somehow.
> 
> 3. Making my own Python WCS downloader algorithm in Python (I think I 
> will need to do this anyway to deliver my project on time, but I prefer 
> more long term solutions for all QGIS users.)
> 
> Any suggestions?
> 
> Kind regards,
> Raymond
> 
> 
> 
> 
> Some data
> 
> 
> This is the GDAL command QGIS generates to clip the extent (2) and the 
> error:
> 
> GDAL command:
> gdal_translate -projwin 148100.0 412300.0 148900.0 411500.0 -of GTiff 
> "cache=AlwaysNetwork&crs=EPSG:28992&format=GEOTIFF&identifier=dsm_05m&url=https://service.pdok.nl/rws/actueel-hoogtebestand-nederland/wcs/v1_0" /tmp/processing_NXPMbm/6597707893384cf9b74c2603ab45909d/OUTPUT.tif
> GDAL command output:
> ERROR 4: 
> cache=AlwaysNetwork&crs=EPSG:28992&format=GEOTIFF&identifier=dsm_05m&url=https://service.pdok.nl/rws/actueel-hoogtebestand-nederland/wcs/v1_0: No such file or directory
> Process returned error code 1
> 
> 
> 
> 
> This is the working WCS, url generated by QGIS and copied from the 
> debugging panel:
> 
> https://service.pdok.nl/rws/actueel-hoogtebestand-nederland/wcs/v1_0? 
> SERVICE=WCS&VERSION=1.0.0&REQUEST=GetCoverage&FORMAT=GEOTIFF&COVERAGE=dsm_05m&BBOX=142327.30414899752940983,408519.58202700602123514,156029.62145483330823481,415020.39733971789246425&CRS=EPSG:28992&RESPONSE_CRS=EPSG:28992&WIDTH=704&HEIGHT=334
> 
> _______________________________________________
> QGIS-Developer mailing list
> QGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer