On 29 May 2008, at 13:17, Dave Stubbs wrote: > On Thu, May 29, 2008 at 9:07 AM, SteveC <[EMAIL PROTECTED]> wrote: >> if the polygon is p1,p2,p3,p4... >> >> c = centre point of polygon >> >> v1 = the vector from c to p1 (p1 - c) >> v2 = the vector from c to p2 (p2 - c) >> >> take the cross product of v1 and v2 >> >> http://en.wikipedia.org/wiki/Cross_Product >> >> if its positive in the z axis its one way, if its negative its the >> other >> > > This only works for nice, simple polygons, of the type that are > probably few and far between in OSM data. It'll work on roundabouts > though which is my major use case for potlatch. The algorithm FAQ had > a nice way using the cross product that will work for all polygons, by > requiring some careful point selection.
oh any polygon where the center of mass is outside of the area covered, gotcha > > > Dave > Best Steve _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
