[OSM-dev] Nested relations and generic implementation of geometry constructs - Was :osm2pgsql patch for nested relations
sly (sylvain letuffe)
liste at letuffe.org
Fri Mar 2 17:15:40 GMT 2012
On vendredi 2 mars 2012, Peter Körner wrote:
> By defining algorithms to work with relations in one place and mapping
> relation-types to that algorithms in another place.
The idea looks sexy, but relations have so many different construction that
you will probably end with as much algorithms as there are relation types.
> For example:
Let's see what exists :
type=multipolygon --> build-polygon (but waterway=riverbank and some lakes are
constructed with touching outer rings loosing the true geometry, if proper
processing is needed we whould need special tweaks of those cases)
type=multipolygon are note expressly said to allow nested relations
type=boundary --> almost build-polygon, but some members sneaked their way as
subareas while not part of the geometry and roles are different.
In those there are cases where nested relation are forming the geometry
type=site (relation become categories ?)--> build-polygon but only for members
with role=perimeter and tags are pushed down
type=route --> build-linestring but only one route/(blank), and conditionnal
on those backward/forward/north/south/east/west
type=waterway --> build-graph special to handle the main stream and the side
streams to build a graph and not a linestring (special handling at GIS side
because it doesn't exist as valid WKT)
type=street/associatedStreet --> build-linestring with role conditions
There are others, but each might need some special roles conditions and the
way tags apply to what might be kind of special
> The goal should be reducing the number of algorithms and re-using them
> as much as possible.
I understand the goal, but fear that it won't be so easy
--
sly
qui suis-je : http://sly.letuffe.org
email perso : sylvain chez letuffe un point org
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