GRASS 6 algorithms not working

[j08lue]

The recent WOIS and GWA installation packages include both GRASS 6 and GRASS 7 together with QGIS 2.18.9.

All paths in the Processing Toolbox settings are set correctly

Despite this, GRASS 6 algorithms cannot be run:

This is a problem particularly due to the widespread use of r.mapcalculator in many of the workflows.

[j08lue]

The problem strictly speaking has nothing to do with the WOIS installer, because it also occurs in QGIS installed with standalone OSGeo4W.

[j08lue]

We tried a couple of things:

• Check on clean OSGeo4W QGIS 2.18.9 installation – error exists already here
• Check with QGIS stock processing toolbox (instead of the WOIS adapted version) – error
• Disable GRASS’s installation check – the algorithm can now be executed but it fails (invalid map)

[j08lue]

The error might have to do with the constellation of packages installed from OSGeo4W, because on some machines with the same versions of GRASS and QGIS but different sets of packages installed, the GRASS 6 algorithms do work.

Also, on a machine with QGIS 2.18.7 and about the same packages installed, the error also occurs.

[radosuav]

Two most suspect packages would be GDAL and GRASS plugin. On my machine I have the latest version of GDAL (2.2.0) and the GRASS plugin installed but for some reason it fails to load properly. GRASS 6 algorithms execute fine in Processing.

Maybe check if the problem computers have GRASS plugin installed and loaded and if GDAL is not up to date.

[j08lue]

@radosuav you were right that the issue was because of GDAL: The OSGeo4W installer does not automatically include the gdal110dll package when installing GRASS 6. @KittelC found out in DHI-GRAS/qgis-processing-swat#14 that this was the cause of this issue.

So users who have this issue need to install just that package (5 MB download) by running the OSGeo4W setup and selecting the package:

We will report this to OSGeo.