On Wed, 26 Oct 2011, Hadley Wickham wrote:
I have a shapefile with a number of line features. I can load it and plot
it. Is there an easy way to downsample or smooth the shapefile to a coarser
resolution?
?gSimplify in rgeos?
Is there a reason that gSimplify doesn't default to a topology
preserving simplification?
Hi Hadley,
GEOS is neutral, and the GEOS nomenclature is misleading IMO. Because the
process treats each ring (polygons) separately, all that is preserved are
the nodes where three rings touch, but not the boundaries between two
polygons, which may generate empty slivers, or overlap. I would have taken
the term to imply that if input rings shared all boundary points between
nodes, then they would be simplified identically, but this is not the
case. To get this (desirable) behaviour, you need a topological vector
GIS, like GRASS. Since I feel that the GEOS name is misleading, the
default is FALSE, but I'm open to better ideas.
Roger
Hadley
--
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: roger.biv...@nhh.no
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