[OSM-dev] Relations, landuse, and gml2osm mess

[Iván Sánchez Ortega]

Hi all,

I've been updating my gml2osm script during all day, feeding it with the Naga 
City data, which is in the public domain. Re-read the "talk" list for more 
info on that data.

You can download the resulting .osm file (can be opened in JOSM, etc) from 
http://blackspark.homelinux.net/landuse2000.osm - please be kind with my 
crappy *DSL upload bandwidth.


My problem is, I've converted a bunch of multipolygons from GML, defining the 
land use. And:
- They are "areas with holes".
- Every area boundary overlaps every other.

Seeing that I'm duplicating the number of neccesary ways (and using every node 
in two different, overlapping ways), my questions are:



Woudln't it make sense to use relations to build polygons for any kind of 
area, thus reusing ways?

The ways should then be the edges of a graph, the graph nodes being nodes with 
three or more ways diverting from then, and any areas would be the graph 
loops.

(Using that model would even simplify by half some steps of rendering, such as 
bezier-curve-hinting area boundaries)



If I use a relation of ways (making up a ring) as the outer (or inner) hull of 
a multipolygon relation[2], will it work?


[1] http://wiki.openstreetmap.org/index.php/Relations/Proposed/Boundaries
[2] http://wiki.openstreetmap.org/index.php/Relations/Multipolygon

-- 
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Iván Sánchez Ortega <ivansanchez at escomposlinux.org>

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