[OSM-dev] multipolygons - dealing with topology errors

[Tels]

On Tuesday 21 July 2009 09:59:29 Jochen Topf wrote:
> 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.

With Temap, I found it is much better to draw such things in bright red, 
that way they get fixed much much faster than when you just drop them - 
out of the sight, out of the mind :)

All the best,

Tels

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