[OSM-talk] Generate polygons out of administrative Relations

[Frederik Ramm]

Hi,

On 28.12.2017 10:37, Nic wrote:
> I want to generate a polygon out of the different members/ways of an
> administrative relation (e.g. Bundesland).
> For that purpose I have loaded a pbf file via osmosis into a
> postgresql/postgis database.

That makes things unnecessarily difficult. Use osm2pgsql to load the
data instead, and the polygons will be built for you. You can even use a
so-called "style file" with osm2pgsql that will only import boundaries,
leaving out roads, buildings etc., which will speed up the process a lot.

> However it seem that the random order of relation members causes
> trouble generating a "simplified" (st_linemerge) linestring suitable to
> apply the st_makepolygon funktion to it.

If you insist on continuing down your path, then st_polygonize would be
the function to use (it does not depend on the ordering of segments),
but osm2pgsl is really the better approach because it builds the
polygons on a "topological" level (using OSM node IDs) instead of on the
geometric level (looking only at coordinates).

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"