[GRASS-user] v.select output vector is empty

[Kevin Webb]

Thank you for your reply Hamish.

2 questions based on your suggestion...


At 11:18 PM 10/29/2008, Hamish wrote:
>Kevin Webb wrote:
> > I am attempting to execute a "point-in-polygon" process on 2 vectors using
> > v.select and the output vector is empty, it contains no value/s.
>
>most likely one of both of the inputs is missing category numbers.
>
>if areas do not have centroids you should add them with v.centroids.
>In general add cat numbers to features with v.category.

Your suggestion to use v.category worked, v.select on the output vector 
from the
v.category command yielded a result.


1.) Why does a 'cat' column show in both vectors but v.select doesn't work 
until
v.category is executed?

Both vectors have the 'cat' column and a visual check of the contents of the
attribute tables for both vectors show a cat value for all records.

GRASS 6.4.svn (lat_lon):~ > v.info -c single_point
Displaying column types/names for database connection of layer 1:
INTEGER|cat
CHARACTER|batch_id
DOUBLE PRECISION|decimal_la
DOUBLE PRECISION|decimal_lo
GRASS 6.4.svn (lat_lon):~ > v.info -c PREC0101
Displaying column types/names for database connection of layer 1:
INTEGER|cat
INTEGER|ID
INTEGER|GRIDCODE
CHARACTER|INCHES


2.) How should I copy/transfer the ID|GRIDCODE|INCHES vector table data 
from the
source vector to the output vector created by the v.category command?