[OSM-dev] Storing node locations on ways

Christoph Hormann chris_hormann at gmx.de
Wed Apr 20 16:59:35 UTC 2016


On Wednesday 20 April 2016, Jochen Topf wrote:
>
> Adding node locations to ways is a pain (and needs more than 32 GB
> RAM these days for a full planet if you want to get it done in
> reasonable time). So I experimented with adding the node locations to
> the ways once and storing it in the OSM files. Works for XML, PBF,
> and OPL. See my blog post at
> https://blog.jochentopf.com/2016-04-20-node-locations-on-ways.html
> for the full story.

From perspective of database design this of course introduces redundancy 
in the data which in turn bears the risk of introducing 
inconsistencies.  For storing data temporarily during processing this 
is not generally a big deal because the processes writing and reading 
this data are well defined but as a general data exchange and storage 
format this would be highly problematic - depending on how a program 
reads the file it will potentially get different results if there are 
inner inconsistencies in the file.

On a more general note: for the purpose of storing the OSM planet data 
in a form that is efficient to use and update wouldn't it make sense to 
store the node locations in a flat file separately from the rest 
instead of storing everything in a dynamically structured format like 
XML or PBF that can essentially only be read sequentially?

Another thing: you say you throw away untagged nodes that are not member 
of any way - don't forget nodes can also be relation members.  I don't 
know any practical case where an untagged node is a relation member but 
in principle this is possible and could make sense.

-- 
Christoph Hormann
http://www.imagico.de/



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