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

[Moritz Lennert]

On 04/11/08 17:57, Kevin Webb wrote:
> 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.

Just because there is a cat column in the attribute table does not mean 
that the actual features have category numbers. To check that you can 
compare the output of v.category option=report ("count" column) with the 
output of v.info -t.

Moritz