[OSM-talk] Valid geometry for closed ways

[Jukka Rahkonen]

Frederik Ramm <frederik <at> remote.org> writes:

> 
> Hi,
> 
> Iván Sánchez Ortega wrote:
> > If you want polygons to behave as in "paleo" GIS, you should refer to the 
> > industry standars. Specifically, to 
> > http://www.opengeospatial.org/standards/sfa , version 1.2.1, page 26:
> 
> Agree with all, except that, for simplicity, we tend to make an 
> exception in
.....
> +------------+
> |  +--+--+   |
> |  |  |  |   |
> |  +--+--+   |
> +------------+

.....

As well as in

+----+---+----+
|    | a |    |
| b  |   |    |
|    +---+    |
|             |
+-------------+

That is, the inner ring touching the outer ring in more than one point. That
situation is a bit complicated to handle with OGC simple features. It would mean
drawing an U-shaped "b" and a box shaped "a" and combining then into an OGC
multipolygon with two outer rings.