[R-sig-Geo] line segments of boundaries
Roger.Bivand at nhh.no
Wed Mar 14 10:42:14 CET 2007
On Wed, 14 Mar 2007, Edzer J. Pebesma wrote:
> Is there an R package/function that, given a set of polygons (say
> country boundaries) finds the line set of lines that defines the
> boundary for each pair of neighbouring countries?
poly2nb() in spdep only finds *polygons* sharing one/two boundary points,
it does not do the topology by breaking the polygons into arcs and nodes.
If you need the topology, I suggest that you establish a GRASS location,
read the vector polygons into GRASS 6, best 6.3 CVS, which will build the
topology - it may need cleaning and repair - then look at vect2neigh() in
the spgrass6 package. This does most of what is needed to retrieve IDs of
neighbouring polygons, and the length of their boundaries. If I recall
correctly, it aggregates multiple boundaries between the same pair of
polygons, which may not suit your case. The ideas and changes in GRASS
were made by Markus Neteler.
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e-mail: Roger.Bivand at nhh.no
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