[R-sig-Geo] Counting points within polygons

[Maria Zwart]

Hi,

There is an easy way to do this, but it is outside R. I use GME (geospatial modelling environment). It can also run R commands however.

The function in that program you are looking for is: countpntsinpolys
More information on: http://www.spatialecology.com/gme/gmecommands.htm

Best,

Mieke

>-----Original Message-----
>From: r-sig-geo-bounces at r-project.org [mailto:r-sig-geo-bounces at r-
>project.org] On Behalf Of Agustin Lobo
>Sent: 18 October 2011 15:25
>To: r-sig-geo
>Subject: [R-sig-Geo] Counting points within polygons
>
>Hi!
>
>Given a Sp Points DF and an Sp Polygons DF, I want to add a field of
>number of points for each polygon
>to the Sp Pol. DF table. This is what I'm doing (using objects from
>the help page for sp::overlay()
>(meuse is the Sp Points DF and srdf the Sp Pol. DF)
>
>> delme3 <- overlay(meuse,srdf)
>> delme3
>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
>1 1 1 1
> [38] 1 1 1 1 1 1 2 1 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3
>3 3 3 3
> [75] 3 3 3 3 3 3 3 3 2 1 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2
>2 2 2 2
>[112] 2 2 2 2 2 2 3 2 2 2 2 2 1 2 2 2 2 1 1 2 2 1 2 2 2 2 3 3 3 3 3 3 3
>3 3 3 3
>[149] 3 3 3 3 3 3 3
>newdata <- data.frame(srdf at data,nppoints=table(delme3))
>srdf2 <- srdf
>srdf2 at data <- newdata
>
>An alternative:
>newdatap <- data.frame(meuse at data, nbp=rep(1,nrow(meuse)))
>meuse2 <- meuse
>meuse2 at data <- newdatap
>delme4 <- overlay(meuse2[,13],srdf,fn=sum)
>newdata <- data.frame(srdf at data,nppoints=delme4)
>srdf2 <- srdf
>srdf2 at data <- newdata
>
>I wonder if there is a better way or, best, an standard R spatial
>function doing that already.
>
>Thanks!
>
>Agus
>
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