On 06/16/2010 06:55 PM, Jenny Turner wrote:
Hi Micha and GRASS-users/list
Let me see if I get this straight
1- use v.digit (e.g. v.digit -n map=vector00 bgcmd=d.rast
map=lsat5_1987_40 )
2- Inside tcltk's digitizing menu select Digitize new Centroid
3- Leave layer as 1?
4- Change Mode to Manual Entry?
All the above looks good.
5- And for each Centroid I select a Cat right?
Yes, always using the *same* cat for training areas of the same type.
(Is this the proceeding?)
About this, I have two questions:
a- I have to leave "Insert New record into table" checked right?
Yes
b- After I left "Insert New record into table" checked, Layer 1 and
Cat 1 and Mode: Manual Entry, when I presss in the image a Error
Window appeared stating: Database table for this layer is not defined.
Where shall i define the database table for a new vectorial that I
digitizing?
Ah, v.db.addtable vector00 col="train_lbl varchar(16), GRASSRGB varchar(16)"
THis should setup an attrib table with two columns, one for a label and
one for an RGB color for the training area.
c- When I press the image a point is created but how can I define the
boundaries of the centroid?
First digitize the boundary. Here you need not enter any attributes. The
cat values are also not relevant.
NExt digitize a centroid inside each boundary. Give each centroid a cat
value that matches the type of training area. So all the forests will be
i.e cat=1, and all the urban will be i.e cat=10, etc.
Thanks
Jenny
On Wed, Jun 9, 2010 at 7:06 PM, Micha Silver <[email protected]
<mailto:[email protected]>> wrote:
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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Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
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