On Thu, Jul 12, 2012 at 12:17:01PM -0700, pcr...@pcreso.com wrote: > Coming from New Zealand, near 180, I think it is fair to say that a geometry > with > left lon > right lon is not wrong. Just that Postgis fails to interpret such > correctly.
Right, is just that PostGIS GEOMETRY has X and Y, not "longitude" and "latitude". > A polygon such as POLYGON((179 -45,181 -45,181 -46,179 -46,179 -45)) > is obviously crossing the dateline, and is geographically identical to > POLYGON((179 -45,-179 -45,-179 -46,179 -46,179,-45)) Why would they be identical ? What makes you think the second one wraps the smaller area including the dateline rather than the larger one not including it ? If you want, a BOX could contain more semantic about this, as it would always tell that it encloses the portion between MIN and MAX. With a POLYGON is harder. And we're still talking only about GEOGRAPHY here, where the knowledge about being on a spheroid is present. > However it is not interpreted as such.This is not a problem unique to > Postgis, and the casting of geometries to geographies, and vice versa for > some geography functions, means that in Postgis, the geography datatype is > still not a complete solution. > > It is a topological as well as a geometric problem. Polygons crossing 180 > need to be split/merged, not just "moved". Right. I've made such a splip/merge function some time ago, it's on the tracker waiting for someone to bring it down to C (WrapX, IIRC). --strk; ,------o-. | __/ | Delivering high quality PostGIS 2.1 | / 2.1 | http://strk.keybit.net - http://vizzuality.com `-o------' _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users