[GRASS-user] "Spatial joining" in GRASS?

[G. Allegri]

This could help: http://wiki.iosa.it/spatial_analysis:feature_count

2008/12/8 Alex Mandel <tech_dev at wildintellect.com>:
> Jonathan Greenberg wrote:
>> I was hoping for a "crash course" in performing a spatial join between a
>> polygon and a point layer in GRASS.  I want to know, for each polygon in
>> vector A, how many points from vector B fall within it, and the average,
>> min, max and stdev of several numeric fields of those points from vector
>> B falling in a given polygon from vector A.  I was trying to do this in
>> Arc but (surprise surprise) it keeps crashing...
>>
>> --j
>>
>
> I can think of several ways to do this, though I haven't tried to do any
> of things I'm about to mention.
>
> The most elegant seems to be:
>
> 1.v.what.vect
> http://grass.itc.it/grass63/manuals/html63_user/v.what.vect.html
> Create a column in the point layer to hold the polgyon id then use this
> command to populate it based on the polygon layer. Once you have that
> you can sum, avg, min, max with sql on the point table and group by
> polygon id which let's you link it back to the polygon layer as a 1:1.
>
> Other things to look at
> v.patch
> v.distance
> v.overlay
>
> Note specifically for you and other UCDavis affiliates we have a copy of
> the GRASS book in the library(currently checked out) and have access to
> the springer digital version.
> http://www.springerlink.com/content/j21632/ just log into the library
> proxy/vpn first.
>
> Of course this could also be done in PostGIS and possibly Spatialite
> SQLite(Testing that right now) with a single query.
>
> Alex
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