[OSM-talk] What's wrong with this multipolygon?

[Zeke Farwell]

Nathan,

I have run into similar issues with complicated multipolygons rendering just
find in Mapnik but not fine in Osmarender.  Another mapper (who's area I had
temporarily broken) told me that the member ways of my relations were in the
wrong order.  At the time I primarily used Potlatch which does not show an
order for relation members.  As far as I knew there was no order, or at
least it didn't matter.  As you know, Mapnik will render multipolygons
correctly as long as all the ways form complete rings and are tagged with
"outer" and "inner" as needed, but it turns out that Osmarender also needs
the ways making up each ring to be in consecutive order.  JOSM shows the
order of the ways and it also shows when they are ordered consecutively in a
ring.

On the multipolygon page of the
wiki<http://wiki.openstreetmap.org/wiki/Multipolygon#Usage>it states
that the order of the ways does not matter, but clearly to
Osmarender it does.  Either this is a bug in Osmarender or the wiki is
wrong.  If you look at my area of the map:
http://www.openstreetmap.org/?lat=44.493&lon=-73.24&zoom=11&layers=M  you'll
see that the large lake (Lake Champlain) renders just fine in Mapnik, but
switch to Osmarender and it looks like hell.  This is most likely because
the outer ways making up the multipolygon are in the "wrong" order.  One of
these days maybe I'll fix it, but I'd prefer it if Osmarender just behaved
in the same way as Mapnik.

Zeke
Burlington, VT


---------- Forwarded message ----------
From: Nathan Edgars II <neroute2 at gmail.com>
To: talk at openstreetmap.org
Date: Thu, 26 Aug 2010 22:10:09 -0400
Subject: [OSM-talk] What's wrong with this multipolygon?
http://www.openstreetmap.org/?relation=1141252
Mapnik has no problems with it, but Osmarender won't fill the northern
part correctly. (It's not a delay in rendering; I added the swamps
after creating the multipolygon.)
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