On Mon, Sep 15, 2014 at 11:21:55PM +0300, Mika Heiskanen wrote: > Hello Sandro, > > I just checked this page: > > http://en.wikipedia.org/wiki/Well-known_text > > Quote: > > It's useful to note that the OGC standard definition requires a > polygon to be topologically closed. It also states that if the > exterior linear ring of a polygon is defined in a counter clockwise > direction it will be seen from the "top". Any interior linear rings > should be defined in opposite fashion compared to the exterior ring, > in this case, clockwise.[1] > > Strange. I did not know the winding rule could be left so arbitrary. > However, if the statement is true, should not GEOS also enforce a > winding rule?
Reading the actual document (06-103r4): http://portal.opengeospatial.org/files/?artifact_id=25355 While there's a mention of this "opposite direction" for shell and holes there's no trace of that requirement in the list of assertions that define polygons as "valid". That said, there's a "normalize" function in GEOS that ensures exterior ring is clockwise and holes are counterclockwise (thus, according to the OGC document, making the polygon be viewed from the "bottom"). --strk; () ASCII ribbon campaign -- Keep it simple ! /\ http://strk.keybit.net/rants/ascii_mails.txt _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel
