[R-sig-Geo] Alternate methods: Polygon Algebra / Polygon Overlay with R Spatial objects..

[rick reeves]

Hello List:

I have been reviewing techniques within R for performing the GIS-like 
operation
'polygon algebra'  (computing the union and intersection of polygons within
two SpatialPolygonDataFrame objects). The goal is to combine two polygon
data frames, to produce a new polygon data frames that contain the union
or intersection of the two input sets.

Thus far, the only method that I have found for this is the combinePolys()
method within the PBSmapping package. The PBSmapping routines work
well, but require the transformation out of the SpatialXXXDataFrame classes.

The overlay() method within sp seems like the best routine for this job 
as it
performs intersection operations on pairs of Spatial objects, but it
does not appear to operate on two SpatialPolygonDataFrame objects.
So I have not tried to use it for this.

Do other packages contain polygon algebra routines that operate on the 
Spatial classes?
If not, are there any alternatives to the PBSmapping methods?

Thanks,
Rick R



-- 
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