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On 2012/08/15 12:40, Micha Silver wrote:
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite">
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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. <br>
</blockquote>
Yes<br>
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite"> 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. </blockquote>
yes<br>
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite">The
full options for v.to.rast (not available in the QGIS GRASS
plugin, only in GRASS itslef)</blockquote>
Ah, confirmation! I was thinking to go to linux - any comments on
which is the better to use?
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite">
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>
</blockquote>
This is new, thanks. This could be a missing link.....
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite"> <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>
</blockquote>
In the process (with this interface) it does complain about a
colours column that it needs extra - have tried a few different
methods there.<br>
Indicates it made it sucessfully but 'couldn't resolve the colour
table issue' (with everything I have tried) - then when you zoom to
that layer you are at the CM's and of course - no colours. But I
didn't know about g.region.vect.....
<blockquote cite="mid:502B7CAE.8040701@arava.co.il" type="cite">
<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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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
052-3665918
</pre>
</blockquote>
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