> So the whole thing is really messy. Indeed... That was an issue many tried to resolve recently - including me: c.f. this thread with a proposal: http://lists.openstreetmap.org/pipermail/dev/2008-July/010937.html I'm still convinved, that OSM deserves a better handling of real polygons... :->
Stefan 2008/11/6 Jochen Topf <[EMAIL PROTECTED]>: > On Thu, Nov 06, 2008 at 09:04:01AM +0100, Till Harbaum wrote: >> i am still not sure i fully understand when exactly a way >> a polygon is. What i've learned so far: >> >> If the first and the last node of a way are identical then the >> way is a polygon, except it's tagged highway, waterway or >> railway. >> >> What's the purpose of the area tag? Does it make a way >> a polygon, even if the first and last node are not identical? >> Is it used to make highways/waterways or railways a polygon? >> >> Should my tool automatically tag a way an area if the first >> and last node are identical? >> >> What about more complex shapes? What if e.g. the first and >> a node in the middle are identical? Is this is polygon with a "tail"? > > You can't say that a way is an area without looking und understanding > the combination of all the tags. > > The only thing you know for sure is: If the first and last node are not > identical, its not an area. And even that is debatable as you mention in > your "polygon with a tail" example. > > And it gets even more complicated with polygons with holes or > multipolygons which need additional relations to model them. So you can > never only look at a way, you also have to check whether there is a > 'multipolygon' relation that includes this way. (And, btw. the > 'multipolygon' relation is misnamed, because it only models polygons > with holes, not multipolygons.) > > So the whole thing is really messy. Everybody is using different ad-hoc > methods to deal with this problem, thats why the renderings of areas > often look different with different renderers. > > Jochen > -- > Jochen Topf [EMAIL PROTECTED] http://www.remote.org/jochen/ +49-721-388298 > > > _______________________________________________ > dev mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/dev > _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
