Hi!
It is possible to extract the centroid coordinates into the database?
(Sorry about my english, I try to explain my probleme). I have a vector
grass polygon data with mysql database connection. But I want use just
the mysql database with the polygons centroid. So that's why I need
upload to the mysql database (like a column) their centroids
coordinates. So it is possible to get this coordinates in Grass??
many thanks: Balazs
2009/9/27 Szabó Balázs <szabobaa@gmail.com>:
Hi!
It is possible to extract the centroid coordinates into the database?
Yes.
(Sorry about my english, I try to explain my probleme). I have a vector
grass polygon data with mysql database connection. But I want use just
the mysql database with the polygons centroid. So that's why I need
upload to the mysql database (like a column) their centroids
coordinates. So it is possible to get this coordinates in Grass??
I would do (untested):
# add new columns
v.db.addcol mymap col="centr_x double precision, centr_y double precision"
# transform coordinates to attributes:
v.to.db mymap type=centroid option=coor col=centr_x,centr_y
# check
v.db.select mymap
This will fail if a category (i.e. attribute row in the table) points to
more than one polygon. In that case, you could add a new table
as layer=2 and populate it with unique values for each polygon
first. Then do above on layer=2 to upload the centroid coodinates
there.
See:
http://grass.osgeo.org/grass64/manuals/html64_user/v.to.db.html
Hope this helps,
Markus