[GRASS-dev] Re: [GRASS-user] How to find whether one vector is contained by another

[Dylan Beaudette]

Hi everyone,

the concept of using geometry index is an excellent idea, and one that is used 
quite often in R: i.e. many functions return the index of matching 
observations- which can then be used for further calculations.

Cheers,

On Wednesday 11 October 2006 12:07, Jeroen Wortel wrote:
> Hi Eric,
>
> you could use a script that goes through the available vector tracks
> and do for each a v.select option=overlap output=dummyfile. The
> contents of the output map are not important, but the fact that it is
> created or not. You could then check in your script if it was created
> or not. If it is created, the vector track touches the polygon
> comprising your region of interest.
>
> A nice addition to Grass would be vector selections that are kept in
> memory instead of written to an output file. Only the pointers to the
> geometry need to be kept in memory, no actual geometry. These
> selection could be used in other grass commands just like normal
> vector maps. This mechanism works for example in GenaMap (called
> active ID's) and is very powerful for scripting purposes and saves a
> lot of temporary files on disk. (This would mean however that vector
> indices should be kept in the vector files instead of created every
> time)that When doing a selection inside or a proximity in GenaMap, the
> number of selected features is returned.
>
> At 20:09 11-10-2006, Patton, Eric wrote:
> >A lot of time I get requests to find out what vector navigation tracklines
> >fall within a certain region. This is easy to do by visual inspection
> >(turning on and off vectors in gis.m) when the number of vectors is low,
> > but becomes too much work for large numbers (i.e., 200). What is the best
> > way to find out if one vector is contained by another, without writing
> > any output? All I need is a listing of vector names.
> >
> >I was thinking maybe set up a bash switch statement to look at a set of
> >cases between the vector's region extents and the extents of the region in
> >question. It seems to me there would be a lot of scenarios to consider and
> >would be really complex (i.e, north_map < north_region && north_map >
> >south_region && ...)
> >
> >Is there any existing vector program that performs this functionality
> >already? If not, what do you think would be the best approach to solve
> > this problem?
> >
> >~ Eric.
> >
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-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341