[OSM-talk] cadastre, ways, rendering

[Jochen Topf]

On Tue, Jan 23, 2007 at 04:33:38PM +0100, Marcus Bauer wrote:
> On Tue, 2007-01-23 at 16:13 +0100, Kristian Thy wrote:
> > On Tue, Jan 23, Marcus Bauer wrote:
> > > That's the reason why ways shouldn't be too long. I.e. for a motorway it
> > > is a good idea to start a new way after each exit. The renderer will
> > > then produce nice maps (and that is what it is all about):
> > 
> > IMO, changing the data to suit the renderer is tackling things the wrong
> > way around.
> 
> Until renderers have artificial intelligence, they will need some help
> to make decent maps. 

They will always need some help, which is ok. Thats why we have the
osmarender:renderRef tag which you can use to suppress rendering of a
ref, for example. At some point the renderer might be more clever and
suppress doubled tags anyway, than we don't need that any more. But
curently we need it and we have it.

But the ref should still be there so that other users of the data can
use it.

> Have a look at this:
> http://www.openstreetmap.org/index.html?lat=43.67615439303823&lon=7.207250585123151&zoom=11
> 
> To avoid this you either add more and more rules to the renderer, ad
> infinitum, or you help it a bit. You don't loose any information if only
> one side of a motorway has a ref=A5 key/value.
> 
> If a highway has more than one ref, like A8/E88, it makes sense to
> alternatingly tag ways, i.e. one section of a highway A8, the next E88.
> You will always have more information to put into the map, but it
> doesn't get better and isn't even of use for later routing, as long as
> it is tagged motorway.
> 
> 
> Another example: how do you make curves? Actually you add points until
> it nicly renders at higher zoom levels. So in a certain way you "change"
> data to suit the renderer.

(Actually you changed the data when you modeled a curve as a group of
straight lines. But thats beside the point. :-)

When you add segments to have a nice curve that surely is for the
benefit of nice renderings, but it does not detract from any other uses
of data. And thats the important point here. Leaving out information like
refs from motorways detracts from non-rendering uses like routing.
Adding more segments to curves is no problem.

Generally having *more* information is always better than having *less*.
It is always easier to delete or ignore information later, but adding
information automatically is hard, because you have to guess.

Jochen
-- 
Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298