On Tue, 26 Jan 2010 16:27:23 +0100 (CET) Roger Bivand <roger.biv...@nhh.no> wrote:
>> For example, I need the distance between points at sea to the nearest >> land area (as defined by for example the 'world' dataset). > > There are methods for point to line segment distances in spatstat. > Further, for projected (planar) coordinates, this could be added to > R-Forge rgeos; for geographical coordinates Boost ggl would be needed. Thanks. The 'nncross' function in 'spatstat' does essentially do what I need. Unfortunately, I work with geographical coordinates (spanning about 15 degrees of latitude), so the results are not perfect (using plain long/lat coordinates), but they will probably be an adequate approximation. BTW, for my application, I'm not interested in the distance per se, only in the points (e.g., boats) within a certain distance from the polygon (land). So I have also thought about a possible solution of using an expanded polygon, expanded in a certain number of kilometers outwards, and then using point-in-polygon (i.e., 'overlay') to find the points that are inside this new polygon. But I couldn't find a function to 'grow' a polygon in this way. -- Karl Ove Hufthammer _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo