[OSM-dev] multipolygon relation and non-closed ways

[sly (sylvain letuffe)]

> Drawing this as one outer ring touching itself in one point seems to
> be invalid for JTS (self-intersection) while drawing an inner ring
> touching outer ring at one point is OK for JTS.

I don't know JTS, but as you describe it, it implements validity as define by 
the OGC for this case.
See here, the "banana polygon" :
http://workshops.opengeo.org/postgis-intro/validity.html

But it shouldn't be forgotten that multipolygons in OSM are not OGC 
multipolygons. 
The sentence used on the wiki since the beginning was :
"multipolygon relation can be used to build multipolygons in compliance with 
the OGC"

In the case 
http://wiki.openstreetmap.org/wiki/Relation:multipolygon/validity#F_-
_Polygon_self_touching_on_one_node
A valid OGC can still be constructed as you described it (one outer and one 
inner touching on one point)


-- 
sly (sylvain letuffe)