[GRASS-user] Point count with large vectors

[Benjamin Ducke]

Don't know if that will speed things up, but you could try
buffering all points in B by a given distance, then use
this to count the points in A that are inside the buffer polygons:

http://grass.osgeo.org/wiki/GRASS_AddOns#v.count.points.sh

You could still do as Hamish suggested to reduce the set of
points to test a priori.

Ben

Hamish wrote:
> Richard wrote:
>>>> I have two large points files (>20,000 sites), and I want to
>>>> find the number of points in A falling within a given distance
>>>> of the points in B.
> ....
>>>> I can use a buffer from Map A and run v.distance, but it takes an
>>>> extremely long time, so suggestions would be welcome!
> ....
>> As to "a long time", I left one loop running for several
>> days and only completed
>> one state of Australia!
> 
> 
> to speed it up perhaps v.buffer + v.select could be used as a
> pre-processing step to remove any points which are too far from both
> A and B? maybe v.buffer for both A and B, v.overlay those two together,
> then v.select only A and B points in that area, and finally run
> v.distance for only the reduced list of points?
> 
> 
> Hamish
> 
> 
> 
>       
> 
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> 
> 


-- 
Benjamin Ducke
Senior Geospatial Consultant

Oxford Archaeology
Janus House
Osney Mead
OX2 0ES
Oxford, U.K.

Tel: +44 (0)1865 263 800 (switchboard)
Tel: +44 (0)1865 980 758 (direct)
Fax :+44 (0)1865 793 496
benjamin.ducke at oxfordarch.co.uk




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