[OSM-dev] [Fwd: Re: Chopped of ways. New flag for OSM XML?]

[Brett Henderson]

Forwarding to list ...

-------- Original Message --------
Subject: 	Re: [OSM-dev] Chopped of ways. New flag for OSM XML?
Date: 	Fri, 15 Aug 2008 06:21:14 +0200
From: 	Rogier Wolff <R.E.Wolff at BitWizard.nl>
Organisation: 	BitWizard.nl
To: 	Brett Henderson <brett at bretth.com>
References: 	<20080812135014.GA29993 at eldorado.topf.org> 
<48A3A7E0.2010503 at bretth.com> 
<52ae42fa0808132155m2bb5ccd3kc9f281481af6c7ec at mail.gmail.com> 
<48A3C659.4060006 at bretth.com> <20080814055626.GA15339 at eldorado.topf.org> 
<48A3E318.9090400 at bretth.com> 
<52ae42fa0808140645t65df93c7mbf160be2fcb8412 at mail.gmail.com> 
<48A440FE.90308 at bretth.com>



On Fri, Aug 15, 2008 at 12:28:14AM +1000, Brett Henderson wrote:
> Karl Newman wrote:
> > On Thu, Aug 14, 2008 at 12:47 AM, Brett Henderson <brett at bretth.com 
> > <mailto:brett at bretth.com>> wrote:
> >
> >     Jochen Topf wrote:
> >
> >         But people *want* to use the data they get from some kind of
> >         extraction
> >         process to base decisions upon. And they should be able to.
> >         Not all the
> >         data is invalidated by an extraction, only some of it. It
> >         makes sense
> >         to mark those parts invalid that are, so that an automated
> >         process can
> >         decide what it uses and what not.
> >
> >         Jochen
> >          
> >
> >     Sure.  If I stop mangling ways then I can't think of a particular
> >     case where this would be useful for osmosis processing ... but
> >     that's not to say one doesn't exist.
> >
> >     I'll keep quiet and let those more impacted by the topic resume
> >     normal discussions ;-)
> >
> > How about Dave Stubb's new tag transform plugin? And the other example 
> > I mentioned, tile cutting, where ways are intentionally mangled to end 
> > exactly on the tile border?
> I didn't explain myself very well.  In the case of these transform tasks 
> you could simply mark the whole file as unsuitable for upload, I 
> couldn't see a case where you'd need to know which entities have been 
> mangled and which haven't.  But again, perhaps I just haven't considered 
> a case where it might be useful.
> 
> If you do need per-entity flagging then 80n's suggestion of fudging the 
> version id (eg. setting to 0) is worth thinking about.

I'm not sure if I understand things fully, but I thought that e.g. for
offline editing you can request the map data about an area from the
mapserver. Say 45.5N to 45.7N, 4.3E to 4.4E. 

Now while "exporting" from the database, the question is: What do you
do with ways that are only partially inside that area? Either you
don't export them alltogether. But in for example an offline editor
this can look very odd: some ways near the edge will be missing
because they are partially outside the selected area.

You can also include nodes outside the area, and deliver complete ways. 

This also looks odd, as at the boundary some ways will continue
outside, and again the temptation will exist to add ways outside the
area, although they are already present in the full database.

So apparently a choice has been made to chop off ways outside the
selected area. 

Those need to be marked in a way that won't interfere with current use
of those ways, as well as inform interested parties/programs that a
more complete way is available on the server.


My personal choice would be to move towards the server delivering all
ways that have at least one point inside the area. If you request two
neighbouring areas some ways will be reported double.... 

	Roger. 

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