Alternate methods: Polygon Algebra / Polygon Overlay with R Spatial objects..
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