Lately I've been using r.grow through the QGIS Processing Toolbox on several rasters which represent the whole world with 500m grid spacing. It takes many minutes to save the output. The reason seems to be that by default, GRASS Processing calls r.out.gdal after the r.grow command to save the output, and it does so with the argument -c createopt="TFW=YES,COMPRESS=LZW". The LZW compression for a raster of this many cells is quite slow, and I don't need it -- I'd rather just have PACKBITS. So, how do I change what it give to createopt? I couldn't find anywhere in the QGIS GUI to change this setting.
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Getting warmer here. The options are specified in github.com/qgis/QGIS/blob/…– foobarbecueCommented Oct 15, 2014 at 0:28
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These options are hard-coded in GrassAlgorithm.py so I just changed them. I'll probably write a fix for this (put it into the Processing settings) if I get the time.
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1BTW: When using GRASS GIS 7 instead of GRASS 6, you can use r.external.out to generate GeoTIFF (or whatever) right away: grass.osgeo.org/grass70/manuals/r.external.out.html - this speeds up things. Example workflow at grasswiki.osgeo.org/wiki/WPS ("WPS workflow idea")– markusNCommented Oct 20, 2014 at 12:10