[OSM-dev] Polygons in OSM don't necessarily comply to simple feature specification

Martijn van Oosterhout kleptog at gmail.com
Thu Apr 17 10:04:07 BST 2008

On Wed, Apr 16, 2008 at 11:28 PM, Martijn van Exel <mvexel at gmail.com> wrote:
> The only exceptions apparently
>  being that self-intersecting polygons are allowed in OSM. He found a
>  couple hundred in the Netherlands' OSM data.

Option 1: Fix them
Option 2: Provide a list so someone else can fix them
Option 3: Provide an example so I can look and see if there's an easy
way to detect them

Seriously though, it's probably a bug that should be fixed. The tools
are there, mostly we just don't know how to use them. For example,
while writing the coastline checker I found that libshp has a
RewindObject function which takes a polygon and fixes all the rings.
Neither my program nor mapnik cared either way, but other products may
not be so lucky.

FWIW, self-intersecting polygons generally don't render well, so some
examples would give an idea of what to look for.

Have a nice day,
Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/

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