[R] Winding Number

[Clint Bowman]

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
> > 
> > 
> 
> 

-- 
Clint Bowman			INTERNET:	clint at ecy.wa.gov
Air Quality Modeler		INTERNET:	clint at math.utah.edu
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