[OSM-dev] Extracting just national boundaries

marqqs at gmx.eu marqqs at gmx.eu
Sun Aug 7 19:12:48 BST 2011


Hi Curt,

> 1.Run: Read all relations and store their dependencies (maybe in a very
> simple database, or even in RAM)
> Then figure out which relations you *really* need.
> 2. Run: Filter these relations.

This is a good description of osmfilter's algorithm. ;-) The program stores the interrelation dependencies in a temporary file and parses this file up to 12 times.

> If I have enough time (likely I won't) I might try to write an osmosis
> plugin for this.

Why? I thought, Osmosis would already be able to perform this task...?

Markus


-------- Original-Nachricht --------
> Datum: Sun, 7 Aug 2011 19:25:51 +0200
> Von: Curt Nowak <nowak at bwl.uni-hildesheim.de>
> An: "dev at openstreetmap.org" <dev at openstreetmap.org>
> Betreff: Re: [OSM-dev] Extracting just national boundaries

> Hello Igor and Peter,
> 
> I'll take a look into --cascading-relations. Maybe I can adapt something
> from there.
> I'm thinking it should be possible in two consecutive runs over a pbf/osm
> file:
>  
> 1.Run: Read all relations and store their dependencies (maybe in a very
> simple database, or even in RAM)
> Then figure out which relations you *really* need.
> 2. Run: Filter these relations.
> 
> If I have enough time (likely I won't) I might try to write an osmosis
> plugin for this.
> 
> Thanks for your help.
> 
> Curt
> 
> ________________________________________
> From: Igor Podolskiy [igor.podolskiy at vwi-stuttgart.de]
> Sent: 06 August 2011 17:44
> To: dev at openstreetmap.org
> Subject: Re: [OSM-dev] Extracting just national boundaries
> 
> Hi,
> 
> On 06.08.2011 17:38, Peter Körner wrote:
> > Am 05.08.2011 17:24, schrieb Igor Podolskiy:
> >> Basically, to implement a
> >> --used-relations you need to compute the transitive closure of a
> >> possibly cyclic graph with relations as nodes and memberships as edges,
> >> and this is not trivial if all you have is a data stream and no loops -
> >> which is the Osmosis model.
> >
> > Osmosis does something very similar in its --cascading-relations option,
> > did you try that?
> yes, I know about --cascading-relations, but it's a --bounding-box
> option, not a standalone task. On the other hand, you're right, you
> always could do something like
> 
> --bbox -90,-180,90,180 cascading-relations=yes
> 
> and have something like --used-relations - thanks for the pointer!
> 
> Igor
> 
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