[R-sig-Geo] (no subject)

[rick reeves]

Assuming that this dataset fits within the confines of R, this could be 
done with sp package:  spdistsN1() function
See attached sample solution:

http://nceas.ucsb.edu/scicomp/GISSeminar/UseCases/AssignClosestPointsR/AssignClosestPointsR.html

Hope this helps! RR

Jonathan Greenberg wrote:
> It seems that a raster-based approach would make more sense, rather 
> than the hugely computationally inefficient approach you are 
> suggesting -- how about using a least cost path or euclidean distance 
> approach?  Both are available in many GIS packages (ArcMap, GRASS GIS, 
> etc...)
>
> --j
>
> x wong wrote:
>> dear all,
>>
>>
>>
>> I have a raster GIS map converted to points. Now, I am trying to 
>> calculate
>> the nearest neighbor distance for every point to a cluster of points 
>> within
>> this map. Since the number of points is more than two millions, I am
>> wondering whether there is a computation efficient way to do this.
>>
>>
>>
>> The following is what the data looks like:
>>
>> point_id,x_coord,y_coord,class
>>
>> 675,-821292,6896866,GL
>>
>> 738,-819294,6895866,GL
>>
>> 803,-819294,6894867,GL
>>
>> 804,-818295,6894867,GL
>>
>> 805,-817296,6894867,GL
>>
>> 806,-816297,6894867,RCK
>>
>> 873,-818296,6893867,GL
>>
>> 874,-817297,6893867,GL
>>
>> 875,-816298,6893868,RCK
>>
>> 876,-815299,6893868,RCK
>>
>> 877,-814300,6893868,RCK
>>
>> 878,-813300,6893868,GL
>>
>> 945,-817297,6892867,GL
>>
>> 946,-816298,6892868,RCK
>>
>> 947,-815299,6892868,RCK
>>
>> 948,-814300,6892868,RCK
>>
>> 949,-813301,6892868,GL
>>
>> 950,-812302,6892869,GL
>>
>> 951,-811303,6892869,GL
>>
>> 1021,-816298,6891868,RCK
>>
>> 1023,-814300,6891868,RCK
>>
>> 1024,-813301,6891869,GL
>>
>> 1025,-812302,6891869,GL
>>
>> 1027,-810304,6891869,GL
>>
>> 1028,-809305,6891870,GL
>>
>> 1029,-808306,6891870,GL
>>
>> 1098,-816299,6890868,RCK
>>
>> 1099,-815300,6890868,RCK
>>
>> 1100,-814301,6890868,GL
>>
>> 1101,-813302,6890869,GL
>>
>> ............................................
>>
>>
>>
>> I want to calculate, for example, the nearest distances for all GL 
>> points to
>> the RCK class.
>>
>>
>>
>>
>>
>> X.W.
>>
>>     [[alternative HTML version deleted]]
>>
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>>
>
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-- 
Rick Reeves
Scientific Programmer/Analyst and Data Manager
National Center for Ecological Analysis and Synthesis
UC Santa Barbara
www.nceas.ucsb.edu
805 892 2533