[GRASS-user] Using Tck/tk vector digitizer for training areas

[Micha Silver]

On 06/09/2010 07:48 PM, Jenny Turner wrote:
> Greetings
>
> I'm using WinGRASS (from OSGEO4W installer) to do some supervised 
> classification. Since I'm using winGRASS i.class function is not 
> available neither wxGUI's vector digitizer. So I'm using tcl/tk but 
> I'm a bit confused on using it.
> About the background images I used a discussion from last week 
> regarding this but now.. How can I define a category? I mean, How can 
> atribute a polygon to a certain category?
This indeed is not obvious. What I've done is change the category mode 
from "Next not used" to "Manual entry". This is set in the lower part of 
the v.digit window (in tcltk interface). Now each time you digitize a 
*centroid* for a training area, set its cat value to some standard value 
you choose. For example, you might decide:
train_area        cat
------------------------
forest             1
agriculture        2
urban              9
water             10
....

Now for each training polygon which is a forest, set the cat value of 
its centroid to 1, agri areas will get value 2, and so on for all the 
centroids of all the training polygons. (Note that the cat values for 
the boundary lines are pretty much irrelevant in GRASS's vector model).

When you're done digitizing training areas, you might add another column 
or two to the attrib table for the training areas -
v.db.addcol train_areas col="train_label varchar(16), RGBCOLOR varchar(16)"
then give each centroid cat value a suitable label and an RGB color 
combo, etc.  Makes life easier down the line...

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-- 
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il


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