FW: [GRASS-user] get x,y from <gravity point> of a centroid

[Moritz Lennert]

On 07/03/08 09:19, christian Brandt wrote:
> 
> ----------------------------------------
>> From: chrisbrandt74 at hotmail.com
>> To: epatton at nrcan.gc.ca
>> Subject: RE: [GRASS-user] get x,y from  of a centroid
>> Date: Fri, 7 Mar 2008 08:17:36 +0000
>>
>>
>> Hello,
>>
>> I got the following result when executing the v.category and afterwards the v.to.db for my centroids to load up x,y-coordinates to my database:
>>
>> updating database ... 
>>
>> More elements of category 4, nothing loaded to DB
>>
>> More elements of category 2, nothing loaded to DB
>>
>> More elements of category 3, nothing loaded to DB
>>
>> More elements of category 5, nothing loaded to DB
>>
>> More elements of category 6, nothing loaded to DB
>>
>> More elements of category 7, nothing loaded to DB
>>
>> More elements of category 8, nothing loaded to DB
>>
>>
>> More elements of category 9, nothing loaded to DB
>> 8 categories read from map
>> 8 records selected from table
>> 0 categories read from map exist in selection from table
>> 0 categories read from map don't exist in selection from table
>> 0 records updated/inserted
>> 0 update/insert errors
>> 8 categories with more points (coordinates not loaded)
>>
>> Any ideas what went wrong?

Yes, apparently you have more than one centroid in each category. GRASS, 
therefore, doesn't know which x,y-coordinates to use in a given category 
  as it has the choice between several.

You will have to create unique categories for your centroids. If you 
don't want to change the current category values, you could add a second 
layer and create unique category values there.

Moritz