Hi, I've asked this question on the tagging list, but I guess this wasn't the best place to talk about it since it involves a question of convertion ability for algorithms to go from OSM's definition of multipolygons (MP) to the OGC simple feature MP entity.
I consider the wiki, as a source of information about tagging, to be the main ressource of information to answer "Am I allowed to tag a MP this way or not" To sum it up, the wiki says that a OSM MP should be considered valid if "the multipolygon relation can be used to build multipolygons in compliance with the OGC Simple Feature standard" (with the known deviation of touching inner rings) However, this is a bit confusing for me because this sentence does say "can be used" but I guess with a powerfull algorithm, it is always possible to build a OGC MP from any OSM MP (possibly by droping unclosed ways, re-cutting ways, etc.) even if ending with a empty OGC MP after droping everything (which is valid according to OGC) My guess is that this sentence implies (without saying it) things like if a member way need to be dropped, then it is an invalid MP. Is that so ? Real border case of validity : http://wiki.openstreetmap.org/wiki/Talk:Relation:multipolygon#special_case_of_touching_outer_.28or_inner.29_rings_on_one_or_more_points_only I didn't thought of this case at random but because a well known algorithm used around here (osm2pgsql) doesn't manage to build a valid OGC MP from such a case. But I'm not talking about it to blame osm2pgsql but to ask if complexity arising from such cases should be considered too much for an algorithm, and pushing back the problem to the mapper saying "no, we consider it invalid for OSM please don't do it." -- sly qui suis-je : http://sly.letuffe.org email perso : sylvain chez letuffe un point org _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
