On Mon, 6 Jun 2016, Kumar Mainali wrote:
I am trying to use unionSpatialPolygons() of maptools to eliminate sliver
in species range. I want to dissolve tiny sliver polygons in a shapefile to
bigger polygons as "Eliminate (Data Management)" of ArcMap does. Whereas I
can dissolve polygons that have identical features in the argument "IDs", I
cannot dissolve tiny polygons based on some threshold in area. In fact, the
argument "threshold" has no effect in the output.
Indeed, threshold is not passed through, it was used when the function
used gpclib rather than rgeos; I'm minded to deprecate
maptools::unionSpatialPolygons anyway. Note that the data are in
geographical coordinates, which may very well not be appropriate for the
topological operations you are trying to do. Use rgeos::gUnaryUnion
instead, and refer to this thread:
https://stat.ethz.ch/pipermail/r-sig-geo/2015-November/023667.html
for using rgeos::set_RGEOS_polyThreshold() and friends. They do not,
however, try to guess which of the polygons neighbouring the sliver should
get the extra area, so you'll have to think that through yourself.
Googling for lists:R-sig-geo dissolve slivers gets a fair number of hits.
There is always also the upstream question of where the slivers came from,
and whether the resolution is not in the earlier process - generate a map
without slivers that says exactly what you mean, rather than fudging it
afterwards.
Roger
Input data is available here:
https://www.dropbox.com/sh/a0x5bbo9u60y7is/AAB6RjXHFQKZv-i-t4JclF3ba?dl=0
p.ranges <- shapefile{raster}
(IDs <- p.ranges$style_id)
library(maptools)
unionSpatialPolygons(p.ranges, IDs = IDs, threshold = 1.5)
-- Kumar Mainali
Postdoctoral Associate
Department of Biology
University of Maryland, College Park
ᐧ
--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: roger.biv...@nhh.no
http://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
http://depsy.org/person/434412
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