Routes definitely have a relation to geometry. It is meaningful to ask what the
length of a route is.
Statistically speaking, relations are multipolygons/boundaries, routes,
restrictions, site and associatedStreet.
For collection relations, there’s hardly any of them, generally they make sense
as a GEOMETRYCOLLECTION, and many of them shouldn’t really be there as
relations are not categories
(http://wiki.openstreetmap.org/wiki/Relations/Relations_are_not_Categories)
From: Кирилл Бестужев [mailto:bestou...@gmail.com]
Sent: Thursday, October 25, 2012 1:45 AM
To: Paweł Paprota
Cc: osmosis-...@openstreetmap.org
Subject: Re: [osmosis-dev] Geometries for the relations table of pgsnapshot
What's the use of converting ALL relations into geometries? Much of them have
no relation to geometry - they are collections, routes and so on!!!
Kirill
2012/10/25 Paweł Paprota ppa...@fastmail.fm
Hi Paul,
I've been doing some similar work on aggregating way/node geometries and there
are some questions that need to be answered when considering something like
this:
1. What spatial type to store? OSM relations obviously can contain both ways
and nodes so when you do a simple ST_Union/ST_Collect you will get a
GEOMETRYCOLLECTION of LINESTRINGs and POINTs; GEOMETRYCOLLECTION is a bit
problematic as it is not supported by many PostGIS ST_* functions.
What I've done myself is I convert node points into closed linestrings with two
points (X, X) thus when I aggregate node and way geometries I get a
MULTILINESTRING which is much more useful than GEOMETRYCOLLECTION.
2. What to do about hierarchical relations (that is, relations that have other
relations as members)? Should they be resolved down to nodes/ways?
Paweł
On 10/25/2012 02:37 AM, Paul Norman wrote:
I keep a pgsnapshot database up to date on my home server for a local jxapi
server and also for analysis.
I have a linestring column built for the ways table, but there's no geometry
for relations.
I am wondering what would be involved with getting a geometry column built
for the relations table.
I expect this would slow down updates, but it would be invaluable to for
analysis.
I believe Ian Dees mentioned to me something about some work that had been
done on this.
Is there anything that I could do to help? I have minimal java knowledge and
some postgis knowledge.
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