[OSM-dev] (Multi)Polygon handling

Jochen Topf jochen at remote.org
Fri Jul 13 19:06:29 BST 2012

On Fri, Jul 13, 2012 at 07:53:30PM +0200, Peter Wendorff wrote:
> Am 13.07.2012 18:31, schrieb nimix:
> >Hi, I just has a look at this... Mapnik indeed has no such requirement. But
> >it requires inner rings of multipolygons do be in a different orientation
> >than the outer ring. Hence it is reasonable to ensure that by just making
> >all outers cw and inners ccw.
> That won't work everywhere:
> If a polygon is outer way of multipolygon 1 and inner way of
> multipolygon 2, it would require to be cw and ccw.
> Therefore as long as the way is a way (independent of ~ or part of
> multiple ~ respectively) multipolygons, it's direction can be
> arbitrary and cannot be fixed to be one particular for multipolygon
> restrictions.

Thats not a problem, because the process we are trying to describe here would
create two *independent* polygons here. One where the ring created from the
way is an inner ring and one where it is an outer ring. And they can both be
turned any way you like. The geometries created are not the way any more.

Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298

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