Thank you, Roger. I cannot fix the upstream processes to eliminate generation of these problems. So, I need to deal with the data I got. I tried various online resources including https://gist.github.com/mstrimas/1b4a4b93a9d4a158bce4 and tried: setScales() set_RGEOS_dropSlivers(TRUE) set_RGEOS_polyThreshold()
before performing: gUnaryUnion(p.ranges, id=NULL) This eliminates the slivers but it also dissolves ALL the polygons to get a single polygon. That is not something I wanted. I would like to dissolve only the tiny polygons to the neighboring bigger ones. Any help is very much appreciated! ᐧ Postdoctoral Associate Department of Biology University of Maryland, College Park On Mon, Jun 6, 2016 at 9:24 AM, Roger Bivand <roger.biv...@nhh.no> wrote: > 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 [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
