On Mon, 6 Dec 2004, Brian Menounos wrote:
Hello, I'm interested in determining the longest linear distance in an irregular polygon (and potentially ones with internal holes) and wondering if there is R code to accomplish this? My interest is to develop an automated procedure to calculate the effective fetch for lakes. In a GIS one can clip line coverage based on an irregular boundary to accomplish this task. The PBSmapping function 'clipLines' unfortunately only works with rectangles. Any help would be greatly appreciated.
I suggest looking at the gpclib package. I don't think the functionality you need is there at the level of an R function, but you may find that you can see how the intersect() function for polygons works. The underlying computational geometry library in both PBSmapping and gpclib is the same. Roger
Thanks in advance, Brian Menounos
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Breiviksveien 40, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93 e-mail: Roger.Bivand at nhh.no