thinning a SpatialPolygonsDataFrame
On Wed, 18 Nov 2009, Pinaud David wrote:
Hi Michael, maybe you should try the function dp() in the package shapefiles that is an implementation of the Douglas-Peucker polyLine simplification algorithm.
Note that its help page does warn that it is not topology-preserving, that is that lines are generalised, but that coincident lines (boundaries of neighbouring polygons) may be generalised differently. GEOS offers a topology-preserving line generalisation facility, which ought to take longer but do better than dp(), because it will not lead to visual artefacts (overlapping polygons, interpolygon slivers, etc.). Roger
HTH David Michael Friendly a ?crit :
The Guerry package contains two maps of france (gfrance, gfrance85) which are quite detailed and large in size (~900K). In writing a vignette for the package, there are quite a few figures that use the map multiple times in a layout, and consequently result in huge file sizes for the .PDF files created. For these purposes, the map need not be nearly so detailed. I'm wondering if there is a facility to "thin" the map by drawing it at a lower density of lines in the polygon regions. When I was working with SAS, there was a GREDUCE procedure that did this nicely. thanks, -Michael
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no