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

[Jeroen Wortel]

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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