On 08/15/2012 03:40 PM, Samantha Goodchild-Brown wrote:
On 2012/08/15 12:40, Micha Silver wrote:
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.
Yes
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.
yes
The
full options for v.to.rast (not available in the QGIS GRASS
plugin, only in GRASS itslef)
Ah, confirmation! I was thinking to go to linux - any comments on
which is the better to use?
You should be able to work with GRASS on Linux, Mac and Windows
pretty much equally well. Moving to Linux is probably a good move in
general, although off topic for this list. But I would suggest to
have a look at the OSGeo LiveDVD which is based on Xubuntu and has
just about all the Open Source GIS stuff available today
pre-installed. You can try it out from the LiveDVD, run it in a
Virtual Machine, making the migration to Linux easier, or just go
ahead and install it.
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.
This is new, thanks. This could be a missing link.....
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?
In the process (with this interface) it does complain about a
colours column that it needs extra - have tried a few different
methods there.
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.....
I don't know why the color table issue comes up, but it shouldn't
interfere with creation of the raster. Did you have a look at r.info
and v.info?
Are these known bugs? can someone give me a
workaround? Or fix my methodology if I am making common
dingbat errors.
Thanks
Sam
_______________________________________________
Qgis-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-user
This mail was received via Mail-SeCure System.
--
Micha Silver
052-3665918
This mail was received via Mail-SeCure System.
|
_______________________________________________
Qgis-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/qgis-user
