John Harvey (j...@johnharveyphoto.com) wrote:
It sure would be nice if users couldn't submit bad data. Incorrect
data (wrong street name) takes a human to spot, but bad topology
(doesn't conform to the rules and a computer can verify conformance)
shouldn't be possible to submit. For instance look at this relation:
http://www.openstreetmap.org/browse/relation/542980
Two ways are marked as inners but nothing is inside anything else. The
problem is these kinds of errors present a barrier to entry for anyone
using the OSM data - if you try to write a "by the books" renderer for
this area you get a spill. To render it correctly you have to test
ways marked the inner are actually inside something marked outside.
Mapnik and Osmarender render this area "correctly" so I believe they
have inside/outside tests. NoName doesn't render the outers and
doesn't spill - I believe it detects the error and handles it in a
different way. Maplint doesn't appear to catch this error. If the
code in those three renderers (which catch this error and handle it two
different ways) was instead in the submission engine the OSM data would
be better for it.
A few other examples of the same problem:
269371 169869 532010 532014 533606 940715 111577 361745 107964 222633
554456 541196 302153 188115
(when an inner and outer share an edge point you get the same problem).
John
FWIW, if you process the OSM data with mkgmap you will get warnings
(and permalinks) for multipolygon errors like these. It's a handy
debugging tool.
--
Charlie
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