[OSM-talk] Islands

[Artem Pavlenko]

On 16 Apr 2007, at 12:00, 80n wrote:

> On 4/16/07, Robert (Jamie) Munro <rjmunro at arjam.net> wrote:
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> Artem Pavlenko wrote:
> >
> > 80n,
> > We don't really need all this crossing segments.
> > Please, could you explain to me what's wrong with representing  
> features
> > like 'river with islands' as proper polygons (one exterior and
> > n-interior rings) ? If you want just a small part of a bigger  
> polygon
> > for rendering use _clipping_.
>
> The problem is that none of our existing editors can cope well with
> editing a way that is big and complicated e.g. the whole river  
> Thames as
> a single polygon. If it's multiple polygons, we need a way to join  
> them,
> which is the crossing segments. It's a similar problem to coastlines.
>
>
> No you don't need to join them.  You can use the feature/bug that  
> ways do not require segments to be contiguous.  You can hop from  
> one side of the river to the other and you can hop from the  
> riverbank to an island without needing segments to connect them  
> together.
>
> Logically a way is made up of one or more sub-paths.  Each non- 
> contiguous segment implicitly defines the start of a new sub-path.
>
> If we ever get rid of segments then, in this scenario, the way  
> would become a super-way and each sub-path would become a way.
>
> The concept of a path comprising of sub-paths is well defined in  
> the W3C specifications and the rendering behaviour of such a path  
> is also well defined.  It seems like a good model to use and is  
> better than re-inventing the wheel (unless someone invents a better  
> wheel).
>
> 80n
>

Well, I'm not with you on this one!  Rendering is only one aspect of  
using OSM data. What about spatial analysis? Do you really suggesting  
to re-invent in that area?

Cheers,
Artem

>
>
>
>
>
> Robert (Jamie) Munro
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Artem Pavlenko
http://mapnik.org



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