[R-sig-Geo] sub-selecting spatial data by distance from a different point(set)

[Paul Hiemstra]

Sorry forgot: spDistsN1 is from the sp package.

cheers,
Paul

Paul Hiemstra wrote:
> Hi Sean,
>
> Take a look at the spDistsN1 function to calculate the distances from 
> a single point to all other points. You can then make the subset based 
> on the distance. What could also be an options is to build a polygon 
> that has the radius around the point you are taking the distance from, 
> and then use overlay to find which points are in the radius polygon. 
> This might be faster when using a large dataset. I'm not sure how nto 
> make the polygon, but it should be possible. But you could first take 
> a look at spDistsN1.
>
> cheers,
> Paul
>
> Sean O'Riordain wrote:
>> Good afternoon,
>>
>> Apologies if this seems a basic question but I'm quite new to spatial
>> analysis (1 week now!) and I'm reading and learning as fast as I can.
>> I've read the Spatial Data task view, "Analysing spatial point
>> patterns in R" by Bradley and I've ordered "Applied Spatial Data
>> Analysis with R" - but it hasn't arrived yet...  I've looked and
>> searched - but I'm guessing that I'm not using the right buzzwords...
>>
>> I have a data.frame (call it A) of about 2 million X,Y points each
>> with info with various characteristics, numeric and factor.  I have a
>> separate much smaller data.frame (call it B) of say 500 rows of X,Y
>> and I'd like to be able to pull a subset of A, so that for each B[i,]
>> I will get all rows from A that are within a given straight line
>> distance (i.e. within a short 'as the crow flies' radius).
>>
>> Could somebody please give me some starting hints please?
>>
>> Thanks in advance,
>> Sean O'Riordain
>>
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>
>


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
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