[R-sig-Geo] Re: [R] Winding Number
Timothy H. Keitt
tkeitt at mail.utexas.edu
Fri Apr 2 20:36:50 CEST 2004
Members of this list may be interested in
http://www.vividsolutions.com/jts/jtshome.htm. There is a C++ port asw
well by the postgis folks.
Tim
On Fri, 2004-04-02 at 12:29, Clint Bowman wrote:
> Roger,
>
> Thanks for your reference. Since I can get the polygon coordinates (and
> have the coordinates of my sites, I can cobble together a function that
> will do the trick.
>
> Again, thanks,
>
> Clint
>
> On Fri, 2 Apr 2004, Roger Bivand wrote:
>
> > On Fri, 2 Apr 2004, Clint Bowman wrote:
> >
> > > I have shapefiles for the state climatic divisions for the United States
> > > and read.shape brings them in wonderfully. Now I wish to run through a
> > > list of several thousand observation sites to find out in which division
> > > each is located. I figure that I can compute the winding number for each
> > > site and be done. However a search doesn't find any references and I
> > > can't find a winding number function among the map/tools/stats. I have
> > > the code for an efficient C++ but was expecting that it would already be
> > > implemented as an R function
> > >
> > > Since I haven't used the map/tools/stats collection before, I suspect I'm
> > > overlooking the function and would be thankful for a pointer.
> > >
> >
> > This is work in progress - where all good ideas and contributions will be
> > welcome. If you look on http://sourceforge.net/projects/r-spatial/, you
> > will see an "alpha" package called "sp", which already has a
> > point-in-polygon facility, but which may not scale up to the kinds of data
> > volumes you have, but which invites a spatial query (match polygon?)
> > function between a SpatialDataFrame with point coordinates and a
> > SpatialDataPolygons object (sometime). This is only as source packages so
> > far, so Windows binaries are not yet available.
> >
> > I have used the splancs package inout() function before, trying the points
> > coordinate matrix on each polygon in turn; splancs is available as a
> > Windows binary. This ought to be less "rough at the edges", and in time
> > will be. The immediate solution is to use splancs, but this will not work
> > if the Shapes have multiple polygons. There is a more specialised list for
> > these kinds of questions in addition to r-help:
> >
> > https://www.stat.math.ethz.ch/mailman/listinfo/r-sig-geo
> >
> > and since yesterday (thanks to Jonathan Baron), its archives are also
> > searchable from:
> >
> > http://finzi.psych.upenn.edu/search.html
> >
> > This question hasn't come up there, but maybe we could move further
> > discussion there - posting only for subscribers?
> >
> > > TIA
> > >
> > > Clint
> > >
> > >
> >
> >
--
Timothy H. Keitt
Section of Integrative Biology
University of Texas at Austin
http://www.keittlab.org/
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