[Tile-serving] [osm2pgsql] Add support for site relations (#221)

[dieterdreist]

2014-11-26 19:59 GMT+01:00 Paul Norman <notifications at github.com>:

> while a geometrycollection doesn't have implications of
> this kind (could be scattered around the world)
>
> generally a geometrycollection will be localized as otherwise the
> pre-computed bounding box used for various purposes will cover too much.
>


yes, a geometrycollection of 2 very distant small objects (as a simple
example) will lead to a completely useless (for rendering purposes for
instance) bounding box. While this of course holds true for all kind of
multi-geometries, my stance on this is that a "site" implicitly has limited
geographical extent.


>  Please also note that there are ~130000 site relations and only ~1400
> collections in our db (as of now).
>
> I'm not sure what you're getting at here - how's this relevant?
>

if someone wants to implement a new function to osm2pgsql it clearly has
more benefit if it covers far more cases, and as mappers seem to prefer
site relations to geometry collections it seems more beneficial to the
project to make use of these. An implementation of a more generic geometry
collection would have far less impact on the results (as it stands now,
this might change in the future).



>  A site relation does offer more semantics via roles, you can say where
> the
> ticket office is to enter a site, or where the parking for a site is (even
> if not inside the site perimeter).
>
> None of the geometry types will allow roles. Unless you're proposing
> schema changes, roles aren't relevant
>

I didn't expect osm2pgsql to support these roles, but there can be other
software to support them. It may have importance for the mapper to choose
the site relation because of the semantics it offers, regardless of support
for this particular detail in osm2pgsql - still it is an argument why
mappers do choose the site relation type and not something more generic.

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/osm2pgsql/issues/221#issuecomment-64771128
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