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<div class="moz-cite-prefix">On 15/08/2012 11:17, Samantha
Goodchild-Brown wrote:<br>
</div>
<blockquote cite="mid:502B5B03.7050707@geograph.co.za" type="cite">Can
anyone tell me how to make a training map for supervised
classification using QGIS Grass (1.8).
<br>
<br>
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).
<br>
<br>
</blockquote>
<br>
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. <br>
<br>
Also be sure to run g.region vect=<your training vector map>
before converting.<br>
<br>
<br>
<blockquote cite="mid:502B5B03.7050707@geograph.co.za" type="cite">If
I use Grass GUI (6.4.2) to convert a vector polygon to a raster,
georeferencing gets lost.
<br>
<br>
</blockquote>
That should certainly not be happening. What do you get from v.info
on the input vector, and r.info on that output raster?<br>
<br>
<blockquote cite="mid:502B5B03.7050707@geograph.co.za" type="cite">Are
these known bugs? can someone give me a workaround? Or fix my
methodology if I am making common dingbat errors.
<br>
<br>
Thanks
<br>
Sam
<br>
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<br>
<br>
</blockquote>
<font size="+1"></font><br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
052-3665918
</pre>
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