[R-sig-Geo] Identifying overlapping polygons

[Roger Bivand]

On Fri, 9 Feb 2007, Andrew Niccolai wrote:

> I am still feeling my way around the "protocol" of this list serve, so I do
> not want to clobber the archives with unneccessary communication.  

Andrew,

My feeling is that volume is not unacceptably high, and that with the list
being searchable, for example:

RSiteSearch("query points polygon")

from the R prompt, the usefulness of the list as a record of ideas, hints, 
and answers is substantial. There is also a pretty complete record of 
the last year or so at:

http://gmane.org/info.php?group=gmane.comp.lang.r.geo

> However, I am compelled to say thanks for the quick turn around and the
> extremely helpful suggestions from Greg and Roger.  Thanks and I will
> let you know how it ends up!

Please do so, I'm sure others can benefit from your experience!

Roger

> 
> -----Original Message-----
> From: Greg Snow [mailto:Greg.Snow at intermountainmail.org] 
> Sent: Friday, February 09, 2007 4:27 PM
> To: Roger.Bivand at nhh.no; Andrew Niccolai
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: RE: [R-sig-Geo] Identifying overlapping polygons
> 
> Andrew,
> 
> Util the functionality is programmed in, here is a quick approximation to
> what you want:
> 
> 1. generate a large number of random (or gridded) points within the polygon
> of interest in the first object (sample.polygon function in package sp).
> 2. use the overlay function in the sp package to find out which polygons in
> object 2 the random points fall into.  You know these overlap. 
> 
> If there is a polygon in object 1 that only slightly overlaps a polygon in
> object 2, then you are unlikely to detect that using this method, but your
> statement about controlling the "Partial" indicates that this may be a good
> thing.
> 
> Turning this around and generating the points from object 2 and seeing which
> polygon in object 1 they are in will tell you if the polygon in object 2 is
> completely overlapped by the one in 1.
> 
> Hope this helps,
> 
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at intermountainmail.org
> (801) 408-8111
>  
>  
> 
> > -----Original Message-----
> > From: r-sig-geo-bounces at stat.math.ethz.ch
> > [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Roger Bivand
> > Sent: Friday, February 09, 2007 12:56 PM
> > To: Andrew Niccolai
> > Cc: r-sig-geo at stat.math.ethz.ch
> > Subject: Re: [R-sig-Geo] Identifying overlapping polygons
> > 
> > On Fri, 9 Feb 2007, Andrew Niccolai wrote:
> > 
> > > Hi.  I am relatively new to Spatial-R.  I have two objects that are 
> > > both SpatialPolygonsDataFrame classes.  One is comprised of
> > polygons
> > > from a section of a segmented image and the other is essentially 
> > > circular polygons representing the potential areas that the
> > crowns of
> > > known tree locations might cover.  I would like to identify every 
> > > polygon from the first object (image segmentation polys) that 
> > > completely are even partially (hopefully I can control the
> > "partial" 
> > > threshold) falls within any given polygon from the second object 
> > > (crown areas).  In ArcGIS this can be accomplished using
> > the Identity
> > > application under ArcToolbox.  I was hoping to accomplish
> > the same feats in R.  Any help would be greatly appreciated!!
> > 
> > This is not present yet, but not impossible. If you look in the code 
> > of the unionSpatialPolygons() function in the maptools package, you 
> > will see that it uses functions in the gpclib package. Using similar 
> > ideas to examine either all n by m intersections, or a clever subset 
> > by looking at bounding box intersections first, it ought to be 
> > feasible. You'll need to be prepared to code it, though.
> > 
> > Roger
> > 
> > > 
> > > Andrew Niccolai
> > > Doctoral Candidate
> > > Yale School of Forestry
> > > 
> > > _______________________________________________
> > > R-sig-Geo mailing list
> > > R-sig-Geo at stat.math.ethz.ch
> > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > > 
> > 
> > --
> > Roger Bivand
> > Economic Geography Section, Department of Economics, Norwegian School 
> > of Economics and Business Administration, Helleveien 30, N-5045 
> > Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> > e-mail: Roger.Bivand at nhh.no
> > 
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo at stat.math.ethz.ch
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > 
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no