On 15/08/2012 11:17, Samantha Goodchild-Brown wrote:
Can anyone tell me how to make a training map for supervised classification using QGIS Grass (1.8).

I have successfully made the polygons with label attributes (as a grass vector layer - attribute table now looks the same as the sample datasets from installation) but these attributes are lost when converting to raster. Hence my raster comes out as one cell (one value to region extents).


You should be getting a raster with different cat values for each of the input vector categories.  In the GRASS toolbox is the module v.to.rast.attr which takes a numeric column in the vector attrib table to be used as the new raster categories. The full options for v.to.rast (not available in the QGIS GRASS plugin, only in GRASS itslef) include a parameter "labelcol=" to give the resulting raster categories a text label in addition to the numeric cat value. 

Also be sure to run g.region vect=<your training vector map> before converting.

 
If I use Grass GUI (6.4.2) to convert a vector polygon to a raster, georeferencing gets lost.

That should certainly not be happening. What do you get from v.info on the input vector, and r.info on that output raster?

Are these known bugs? can someone give me a workaround? Or fix my methodology if I am making common dingbat errors.

Thanks
Sam
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