[OSM-talk] Tiles at home Update

Dave osm.list at randomjunk.co.uk
Wed Mar 21 17:35:11 GMT 2007


On 21/03/07, matthew-osm at newtoncomputing.co.uk <
matthew-osm at newtoncomputing.co.uk> wrote:
>
> On Tue, Mar 20, 2007 at 10:14:20PM +0100, Dirk-Lüder Kreie wrote:
> > While I like the new osmarender styles and small fixes I'm against the
> > usage of this preprocessor for the tiles at home layer.
> > The errors should be fixed in the source data, not at the renderer.
>
> Are they errors?
>
> My (probably flawed) understanding of the definition of a
> way is that it is an unordered group of segments. The fact
> that the API returns them in the same order as they were
> uploaded is therefore just coincidence.  Given this, it is
> essential that any renderer can cope with ways that contain
> segments in any order.
>
> On the other hand, maybe the definition actually is
> "ordered" and I missed that bit ;-).



They are ordered, as in the API/DB will return them in the same order they
were uploaded. That's in the spec.
The only problem is that there is no semantics defined as to what that
ordering should be -- it's entirely up to the uploaders. So no, they're not
errors as such, other than they don't render nicely without preprocessing,
and there seems to be a general consensus on what constitutes a nice way for
these purposes, and they aren't it.

Of course, in a future version of the OSM data model it's possible this
might change, at which time they may become errors, but until then
renderers/editors etc will just have to cope (or not cope, with the
intention of making users change things manually, assuming they can actually
figure out what's wrong).

Personally I think coping is the best way to go... OSM data will always be a
little fuzzy round the edges, and not rendering a mess makes sense to me.
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