[R-sig-Geo] thinning a SpatialPolygonsDataFrame
Roger.Bivand at nhh.no
Wed Nov 18 15:43:50 CET 2009
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.).
> Michael Friendly a écrit :
>> 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
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