Nathan Vander Wilt schrieb:
On May 28, 2008, at 1:35 PM, Richard Duivenvoorde wrote:Richard Fairhurst wrote:Can anybody point me in the direction of an algorithm that will determine whether a closed way (polyline) is clockwise or anti- clockwise?Richard, there is a good set of (explanations of) algorithms here: http://www.faqs.org/faqs/graphics/algorithms-faq/If you can treat the earth as a cartesian plane 360 units wide by 180 tall these equations could be used. But be careful here. Lat/lon coordinates actually are based on a more complicated topology. A spherical polygon always encloses a finite area less than the surface area, so the usual method of "checking for negative area" doesn't work out so well.
Our data-model does not support earth as a sphere. -- Dirk-Lüder "Deelkar" Kreie Bremen - 53.0952°N 8.8652°E
signature.asc
Description: OpenPGP digital signature
_______________________________________________ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
