> Hi, > > > eg. we've also decided to add area > > support ;-)? > > Independent of whether or not 0.6 has area support (it's not planned to > the best of my knowledge) - how would you model areas (a) in the SQL > structure and (b) in XML? > > It seems obvious that areas, like ways, need to be based on a sequence > of nodes. (If you were to base them on ways, then that would be nothing > different from today's relations, would it?) > > An area with no holes inside would trivially have the exact same > structure as a way, perhaps using <area> instead of <way>. It would also > omit the last <nd ref="..."> which, for circular ways, is identical to > the first, because for an area it is obvious that the boundary must be > closed. > > <area id="1234" /> > <tag k="landuse" v="industrial" /> > <nd ref="1" /> > <nd ref="2" /> > <nd ref="3" /> > </area> > > Now if the area has holes - and I assume that the area type needs to > take care of that - how would these be modelled? We'd have a number of > "node groups", one of which is the outer boundary, the others would be > inner boundaries. > > One possible XML representation would be to say that the node groups are > numbered, with the outer always carrying the number 0: > > <area id="1234" /> > <tag k="landuse" v="industrial" /> > <nodegroup id="1234-0"> > <nd ref="1" /> > <nd ref="2" /> > <nd ref="3" /> > </nodegroup> > <nodegroup id="1234-1"> > <nd ref="4" /> > <nd ref="5" /> > <nd ref="6" /> > </nodegroup> > ... > </area> > > This structure could be mirrored in the SQL tables, with the > "area_nodes" table having an extra "nodegroup" column. > > Areas could be introduced slowly, by simply allowing them in the API and > not converting anything at first, instead counting on people doing the > conversion with scripts in the time after the switch. Alternatively, > areas could be populated from existing area-ways and multipolygon > relations when they are introduced, but such operations tend to > complicate the deployment of a new API.
Are areas-with-holes really necessary (as primitives)? After all, we don't have multi-ways or ways-with-gaps either... Regards, Marc -- Psssst! Schon das coole Video vom GMX MultiMessenger gesehen? Der Eine für Alle: http://www.gmx.net/de/go/messenger03 _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
