[OSM-talk] Islands

[80n]

On 4/16/07, Robert (Jamie) Munro <rjmunro at arjam.net> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> 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






Robert (Jamie) Munro
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.6 (Darwin)
> Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
>
> iD8DBQFGI1USz+aYVHdncI0RAlVMAJ9+gFeB0q23jLQFlyBHhXfZVod5ygCdGj9F
> r9qMkGs42vUjaOTn7zJsS6k=
> =fMVf
> -----END PGP SIGNATURE-----
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk/attachments/20070416/ff51372c/attachment.html>