On 10/19/2015 5:50 AM, Sven Geggus wrote:
Hello,
looking at the code of osm2pgsql and checking with a hand-crafted .osm file
I came to the conclusion that polygons in osm2pgsql are handled in the
following way:
If a polygon is defined in the .style file a function is called which
generates the simple-feature geometry object. If this function is unable to
generate a polygon a linestring is created.
Am I right in this assumption?
For the osm2pgsql pgsql backend, a polygon is formed when a way is
closed and the tag transform sets a polygon flag. If either of these is
false, it is a linear feature. For the C tag transforms*, the polygon
flag is set when there is a tag which has a polygon flag set, or phstore
which is equivalent to polygon,nocolumn
For the multi-backend, see
https://github.com/openstreetmap/osm2pgsql/issues/270. This issue also
contains some information about the pgsql backend.
The reason for this question is that I'm trying to build a imposm3 style
which will create a osm2pgsql compatible database. This has (among other
things) the obvous advantage, that some additional tables for more exotic
features are easy to create.
osm2pgsql has the capability to arbitrarily convert tags, for example
unit conversions, normalize yes/no/unknown values, transliterate values,
use other PostgreSQL types, and perform other logic. When I looked at
imposm3, it didn't have the capability to take a script. Has this changed?
Even if not using custom tag transforms, the osm2pgsql C tag transforms
do perform some tag manipulation.
* They still get called the C tag transforms, even though osm2pgsql is
C++ now
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