Well, right now, how do I turn a column of MULTIPOLYGON goemetries into a single collected MULTIPOLYGON? I have to rather inefficiently explode them, then re-collect them. Kind of a trivial example.
More fiddly for people to currently solve, the ST_Intersection() function can spit out heterogeneous GEOMETRYCOLLETIONS as a result. And usually, the end-user just wants one component of that... if intersecting lines on polygons, they just want lines, and don't care about any points. Or if doing poly-on-poly, they don't care about any lines or points that fall out the bottom, as occasionally happens. P. On Wed, Jan 28, 2009 at 4:40 PM, Mark Cave-Ayland <[email protected]> wrote: > Paul Ramsey wrote: > >> I would like to add a function that takes an anonymous >> GEOMETRYCOLLECTION and returns something more structured: >> - a GEOMETRYCOLLECTION where the first element is a MULTLIPOLYGON, the >> second a MULTILINESTRING and the third a MULTIPOINT? >> - a tuple, with elements 'polygons', 'linestrings', 'points', each >> with one multi* of each? >> - a tuple, with elements 'polygons', 'linestrings', 'point', each with >> an array of singletons? >> >> The key here is to provide a useful flat structure to pull info out >> of. Some information in the GEOMETRYCOLLECTION *will be lost*, (but >> that seems an acceptable price) >> >> Another approach, which might be simpler for users to grok would be: >> >> ST_CollectionAsMultiPolygon() returns just the polygon elements of a >> collection. >> ... etc ... >> >> Thoughts? >> >> P. > > Hi Paul, > > I'm still struggling to get an idea of exactly what these proposed functions > are trying to achieve. Can you show some potential problems/SQL statements > showing how you would envisage these functions being used? > > > ATB, > > Mark. > > -- > Mark Cave-Ayland > Sirius Corporation - The Open Source Experts > http://www.siriusit.co.uk > T: +44 870 608 0063 > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
