[EMAIL PROTECTED] wrote on 2007-02-09 13:27:13: > 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.
An interesting suggestion, emulating the old manual way of computing the area of a polygon, if you were to use a grid of points whose surrounding areas (Voronoi polygons) were all identical. To deal with "partial", choose the spacing of points (hence areas of Voronoi polygons) to be a compromise between a desired resolution and computation time, depending on how many of these comparisons you need to make. > > Hope this helps, > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > [EMAIL PROTECTED] > (801) 408-8111 > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Roger Bivand > > Sent: Friday, February 09, 2007 12:56 PM > > To: Andrew Niccolai > > Cc: r-sig-geo@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@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: [EMAIL PROTECTED] > > > > _______________________________________________ > > R-sig-Geo mailing list > > R-sig-Geo@stat.math.ethz.ch > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > > > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo