[OSM-dev] planet diff and excerpts

Brett Henderson brett at bretth.com
Thu Oct 11 14:06:51 BST 2007


Frederik Ramm wrote:
> Hi,
>
>     probably a question to Brett H but I think others may be interested.
>
> Say I have a planet extract containing Germany, and I want to keep  
> that up to date using the planet diffs.
>   
I've been wondering about this myself ...
> Then I'll just apply the normal (full planet) diffs to my extract and  
> run a new polygon extraction on the result which will give me the  
> updated excerpt, right?
>   
Yeah, I guess that should work.  I must say I hadn't thought of doing 
this though.  It will rely on the polygon tool being able to copy with 
ways and relations referring to non-existent nodes and ways.  I don't 
think this will be a problem though.
> And afterwards I could diff my old data and my new data and thus  
> create a diff that is limited to the excerpted area.
>   
Yes, that should be possible.
> I don't suppose it would be possible to make something like a polygon  
> excerpt from a diff, because the diff doesn't necessarily contain the  
> location where a change occurred (if the change is e.g. in a way).
>   
Yes, that's the tricky bit.

I've just posted some questions to the "relations without members" 
thread.  I'm curious exactly how the extract-polygon perl script works.  
Osmosis polygon extraction is broken at the moment (I forgot to finish 
it during the 0.5 changes ...), I'm hoping to get it working again but 
if it's become horribly complicated I may have to pull the tasks out 
again.  If relations can contain other relations I don't think osmosis 
will be able to support it because it always works in a streamy fashion, 
working around that will be difficult.

Cheers,
Brett





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