On Jul 22, 2004, at 7:06 AM, Markus Neteler wrote:
On Wed, Jul 21, 2004 at 03:59:41PM -0500, William K wrote:
Or whatever they're called. Right now I'm looking at lines. When you
d.what.vect, it shows cats, fields and attributes, and length and line
height. I haven't checked polgons yet, but I'm guessing they have
perimeter and area instead of length.
1. I would like to v.extract to extract lines above a certain length -
ie weed out those short blips.
You need to use v.to.db.
1. use db.execute create a new table:
Example:
echo "CREATE TABLE roadlength (cat integer, linelength double)" |
db.execute
Link this table as second table to your map:
#check current settings:
v.db.connect -p roads2
#link new table:
v.db.connect m=roads2 dr=dbf
data='$GISDBASE/$LOCATION_NAME/$MAPSET/dbf' \
key=cat table=roadlength field=2
2. Verify that the new tables exists now:
v.info -c roads2
v.info -c roads2 field=2
Odd. Even tho field 2 is used to connect, v.info -c reports field 1
having the DB. v.info -c f=2 says database connection not defined.
But the following steps work. Bug in v.info?
3. Generate new categories in the map:
v.category roads2 out=roadsnew field=2 option=add
v.category input=roadsnew option=report
# should report something like this (for field=2):
# type count min max
# line 825 1 825
# -> 825 lines in this map
Can't do this in-place?
2. I want to export the lines with line height as an attribute. Not
important now, but labelling lines with line height, using different
colors... (not ready to mess with NVIZ yet, but maybe that's the only
way?), or extracting certain line heights or ranges of heights.
... see above (now you should be able to do that).
where do I get the line height from? I didn't see it as an option for
v.to.db.
-----
William Kyngesburye <kyngchaos@xxxxxxxxxxx>
http://webpages.charter.net/kyngchaos/
All generalizations are dangerous, even this one.
