[R-sig-Geo] For each point, distance to nearest point in second dataset

Michael Sumner mdsumner at gmail.com
Fri May 20 03:37:42 CEST 2016

```On Fri, 20 May 2016 at 08:38 Nick Eubank <nickeubank at gmail.com> wrote:

> For other's reference, that was almost right:
>
> To get distance from each voter to closest polling place, the syntax was:
>
> knn.results = knn(data=coordinates(polling.places),
> query=coordinates(voters), k=1)
>
>
>
Great!  Be sure to use the WKNNF approach to cache the kdtree of the data -
it only needs to be done once, but calls to knn obviously will redo that
part.

Also, you'll probably want to do it with coordinates in a map projection
where nearest-neighbour distance makes sense for your domain.

Cheers, Mike.

> On Thu, May 19, 2016 at 3:03 PM Nick Eubank <nickeubank at gmail.com> wrote:
>
>> Thanks Michael!
>>
>> Super easy context: two SpatialPointsDataFrames ("voters",
>> "polling.places"). Each has coordinate columns "x" and "y".
>>
>> Is it just:
>>
>> library(nabor)
>> knn(voters, query = polling.places, k=1)
>>
>> ?
>>
>> On Thu, May 19, 2016 at 2:59 PM Michael Sumner <mdsumner at gmail.com>
>> wrote:
>>
>>> Use nabor package, it takes a little to learn but is crazy fast.
>>>
>>> Happy to show if you make a relevant example.
>>> Mike
>>>
>>> On Fri, May 20, 2016, 06:42 Nick Eubank <nickeubank at gmail.com> wrote:
>>>
>>>> Hi All,
>>>>
>>>> Trying to an equivalent to the "nearest" tool in ArcGIS for two
>>>> SpatialPointDataFrames. I can do the naive implementation by calculating
>>>> all pairwise distances using gDistance and taking the min, but I have
>>>> some
>>>> huge datasets and was looking for something more efficient. (For
>>>> example,
>>>> here's a trick with knearneigh for points in same dataset (
>>>>
>>>> http://gis.stackexchange.com/questions/132384/distance-to-nearest-point-for-every-point-same-spatialpointsdataframe-in-r
>>>> )).
>>>>
>>>> Any suggestions?
>>>>
>>>> Thanks!
>>>>
>>>> Nick
>>>>
>>>>         [[alternative HTML version deleted]]
>>>>
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>>>>
>>> --
>>> Dr. Michael Sumner
>>> Software and Database Engineer
>>> Australian Antarctic Division
>>> 203 Channel Highway
>>> Kingston Tasmania 7050 Australia
>>>
>>> --
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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```

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