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How can I do spatial selections or filters in R? I can do this in PostGIS using (e.g.):

SELECT * FROM mypoint, mypoly
WHERE ST_Within(mypoint.geom, mypoly.geom);

and it is similarly a piece of cake in most other GIS software. So I'd expect something in R to look like:

mypoint[within(mypoint, mypoly),]

but I can't find any leads anywhere. I'm looking for something that uses the common spatial predicate terminology used in PostGIS/GEOS/JTS/Shapely (within, contains, intersects, overlaps, touches, etc.; DWithin would be bonus). Does this functionality or library exist for R? If not, is there something that is similar?

Note: In R, I use the sp class for my objects (SpatialPointsDataFrame, etc).

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1 Answer 1

up vote 9 down vote accepted

For your specific question, you should be able to use point.in.polygon (docs) or overlay (vignette) to perform the analysis.

A spatial predicate language isn't trivial to implement, and all the examples you mentioned boil down to ports or wrappers of JTS at some point. There is a pre-alpha release of rgeos, a recent Google SOC entry which provides access to GEOS directly from R.

In general, it seems that the R developers are grappling with whether they want to maintain a full GIS implementation within R itself, or instead rely on facilitating packages that allow interaction with PostGIS, GRASS (spgrass), SAGA (rsaga) and the like to provide deeper spatial savvy.

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point.in.polygon is a good start for basic polygons, although a bit crude (e.g.): point.in.polygon(pnt@coords[,1], pnt@coords[,2], lake@polygons[[1]]@Polygons[[1]]@coords[,1], lake@polygons[[1]]@Polygons[[1]]@coords[,2]) I'm really looking forward to rgeos that you mentioned, and has all the binary predicates and more. –  Mike T Feb 7 '11 at 20:29
    
For spgrass6 examples with GRASS, see grass.osgeo.org/wiki/R_statistics –  markusN Feb 8 '11 at 7:25
1  
rgeos is now on CRAN, and is very simple to install/use/etc. –  Mike T Oct 11 '11 at 0:20

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