On 02/07/14 16:01, lbianchi wrote:
Hi, this is my first message to the list. I'm using Grass 6.4.3 under
Linuxmint 16.
I'm trying to make a supervised classification.
After digitizing the training areas, I transformed them from vector to
raster. Then I've done the following:
/|g.region
rast=train_area_2013_03_05_raster@PERMANENT,2013_03_05_toar4@PERMANENT|/
I would just use the image as your reference for the region, not the
training areas.
Also, what was the region setting when you converted your training areas
to raster ?
Try first setting your region to the satellite image, i.e.
g.region rast=2013_03_05_toar4@PERMANENT
Then v.to.rast of the training areas, then i.gensig.
You can also use i.class in 6.4.3 (with x-monitor), or g.gui.iclass in
the wxgui in grass7 to check your classes.
Here: http://lists.osgeo.org/pipermail/grass-user/2010-April/055821.html
there's another similar question, but the only answer says: "I suspect
that either the training areas are suboptimal or are too small." What
does suboptimal means? What is an optimal training area? How big should
they be?
I have 30 areas, 10 for each class. They aren't too big because I have a
small site to clasify.
Maybe they are too small ?
What does |"/Signature X not invertible/"| means? Is this the real problem?
Yes. And it's linked to the notion of "suboptimal" training areas.
Training areas should be big enough to contain a significant number of
pixels (i.e. do not use training areas that are only 5 pixels), but
small enough to be homogeneous.
Moritz
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