[R-sig-Geo] (no subject)

[Roger Bivand]

On Wed, 8 Apr 2009, x wong wrote:

> Thank you very much, that is very helpful.
>
>
> x.w.
>
> On Wed, Apr 8, 2009 at 12:47 PM, rick reeves <reeves at nceas.ucsb.edu> wrote:
>
>> 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
>>

Note that this will be inefficient in that it calculates all the 
distances. I have an off-CRAN package interfacing ANN, which - given two 
sets of points, returns the k nearest in the first set (with distances) 
for each point in the second set. ANN builds a tree of the first set, so 
searches for nearest neighbours efficiently. Look for:

http://spatial.nhh.no/R/etc/ann*

The Windows binary wasn't built for the current release of R, so probably 
needs rebuilding - let me know if you use Windows, and I'll re-build it.

Hope this helps,

Roger

>>
>> 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]]
>>>>
>>>> _______________________________________________
>>>> R-sig-Geo mailing list
>>>> R-sig-Geo at stat.math.ethz.ch
>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>>
>>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at stat.math.ethz.ch
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>>
>> --
>> 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
>>
>>
>
> 	[[alternative HTML version deleted]]
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no