I would like to randomly select polygons and I'm not sure how to do it. I've
thought about converting the polygon map into a rast map, then using
mapcalc, but since mapcalc works cell by cell, I won't get the entire
polygon. I'm using GRASS 5.3 since I seem to be having build troubles with
GRASS 5.7 and I don't know how to add multiple attributes to a vector map in
5.3. If I could then, I could perform some type of (and I'm dreaming here)
"select * into rand.trainploys from trainpolys where rand() > 0.5"
I haven't attempted to build 5.7 in some time and can't spend the day
trying.
Thanks,
Jeff.
---
Jeff D. Hamann
Forest Informatics, Inc.
PO Box 1421
Corvallis, Oregon USA 97339-1421
541-754-1428
jeff.hamann@forestinformatics.com
www.forestinformatics.com
I would like to randomly select polygons and I'm not sure how to do
it. I've thought about converting the polygon map into a rast map,
then using mapcalc, but since mapcalc works cell by cell, I won't get
the entire polygon. I'm using GRASS 5.3 since I seem to be having
build troubles with GRASS 5.7 and I don't know how to add multiple
attributes to a vector map in 5.3. If I could then, I could perform
some type of (and I'm dreaming here)"select * into rand.trainploys
from trainpolys where rand() > 0.5"
I haven't attempted to build 5.7 in some time and can't spend the day
trying.
Sorry for the "use 5.7" answer, but if you get it to work, try
v.extract:
"Selects vector objects from an existing vector map and creates a new
map containing only the selected objects."
You'd need to label each polygon from 1+ with v.alabel or something and
use a simple random number generator program to pick a number. Then
v.extract.
Do you just need stats on a random polygon or need to make a whole new
map of it?
What's the problem you're having with 5.7? what kind of computer?
If you can build 5.3, then there shouldn't be anything horribly missing
for a 5.7 build.