[GRASSLIST:10808] Re: How to extract polygons from vector map

[Michael Barton]

Michael,

You should have SOME kind of value attached to the vector--either as cat or
label. You can have r.to.vect create this. You can also run v.category to
add unique cat values to each vector object. Then you can use a query to
extract the one you want.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton



> From: Michael Rensing <michael.rensing at shaw.ca>
> Date: Tue, 07 Mar 2006 19:53:12 -0800
> To: Michael Barton <michael.barton at asu.edu>
> Cc: Multiple recipients of list <GRASSLIST at baylor.edu>
> Subject: Re: [GRASSLIST:10743] How to extract polygons from vector map
> 
> Yeah, that's one way I figured it out. Problem is, I'm generating
> contours from a DEM for a large region, and I wanted to pick one to
> extract. There are no attributes assigned by r.contours that I can use.
> 
> Unless a better idea presents itself, I'm going to create small local
> contours around the lakes, then collect them into a single vector layer,
> add an attribute, and use the form mode of the mouse query to edit the
> new attribute. THEN I can use an attribute query to extract the vectors
> I want.
> 
> There should be a better way, but this does keep me amused...
> 
> Michael
> 
> Michael Barton wrote:
>> In the new GIS Manager (gism2), if you can display only that polygon with an
>> attribute query, you can extract it to a new vector. (See new vector panel
>> with button to extract queried vector).
>> 
>> Michael
>> __________________________________________
>> Michael Barton, Professor of Anthropology
>> School of Human Evolution and Social Change
>> Arizona State University
>> Tempe, AZ 85287-2402
>> 
>> phone: 480-965-6213
>> fax: 480-965-7671
>> www: http://www.public.asu.edu/~cmbarton
>> 
>> 
>> 
>>   
>>> From: Michael Rensing <michael.rensing at shaw.ca>
>>> Date: Sun, 05 Mar 2006 11:18:12 -0800
>>> To: <GRASSLIST at baylor.edu>
>>> Subject: [GRASSLIST:10743] How to extract polygons from vector map
>>> 
>>> I've got a vector map where I can visually identify one outline which is
>>> a lake. How can I extract that one vector from the layer and turn it
>>> into a filled blue polygon in a new layer?
>>> 
>>> You've all been a huge help to me so far, and I hope that the good will
>>> continues until I am able to contribute my own answers. If anyone is
>>> interested in what I'm up to, I've been keeping a sketchy blog at
>>> http://mjr42thoughts.blogspot.com/
>>> 
>>> Regards,
>>> Michael
>>>     
>