[OSM-dev] multipolygons - dealing with topology errors

[Jochen Topf]

On Mon, Jul 20, 2009 at 10:36:21PM -0400, Ben Supnik wrote:
> Two things about multipolygons:
> 
> 1. My software now detects topologically broken multipolygons, e.g. 
> cases where I can't form rings out of the node list.  Is this useful, or 
> is this information already generated by things like pgsql?
> 
> 2. While looking at one test set of data, I found a lake where one 
> island (modeled as a hole in the lake multipolygon) had not been "sealed".
> 
> Mapnik simply ignored the island, but osmarender had linked the start 
> and end of the ways to form the island.
> 
> I have learned from experience that it isn't useful for me to ask 
> "what's the spec"...OSM is its own spec, etc. etc.
> 
> So I'll just ask: any comments?  Is one interpretation considered better 
> or worse than the other?

Depends on what you are doing. When you are generating a map that OSM mappers
will see, its probably better not to draw anything, to encourage people to
fix it. When using the data for maps not related to OSM directly, it might
be better to automagically fix things, because people wont fix it anyway.

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