[GRASSLIST:10810] Re: How to extract polygons from vector map

[Michael Rensing]

Aha! A slightly better way. r.contour seems to create a unique category 
for each altitude, but all contours at that altitude have the same 
category, which was part of my problem. Your suggestion to use 
v.category to add a sequence of unique cat values should do the trick 
nicely. Thanks very much.

Regards,
Michael

Michael Barton wrote:
> 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
>>>>     
>>>>