On 4 Jan 2008, at 13:41, bvh wrote: > On Thu, Jan 03, 2008 at 03:16:47PM +0000, Artem Pavlenko wrote: >> What people think about explicitly supporting curves as a part of >> geometry model? This way we can model the world better. > > I would be heavily in favor of it. IMHO the simplest way to do this > is best. > > What I could see working is something like this : > > we define a standard interpolation method that turns a set of point > into > a sucession of bezier curves. (for an example see > http://www.antigrain.com/research/bezier_interpolation/index.html) > I understand you have already implemented another on the fly > algorithm in mapnik, we could use that as well.
mapnik is using AGG for rendering, so yes, this is exactly what I'm doing :) > > next there is a smooth=yes tag that would mean : apply the smoothing > on this road. > > The big advantage is : no change is necessary on our data model. > Maintained tools can implement support for this on their own pace. > Old tools that don't know about smooth ways keep working. And > since we are only adding capabilities we are sure this introduces > no regressions (ie, everything that worked before keeps on working) > I agree, this is a less destructive solution. > The only disadvantage is that over time, people working with > editors with smoothing support are going to add ways with very > little points, possibly resulting in choppy maps on renders > that don't know (yet) how to deal with the smooth tag. Or an opposite, people will be adding too many vertices in editors that are lacking support for bezier interpolation.. > >> P.S. Are there some hints (tags) in OSM that can be used for to >> smooth or not? > > No, so I proposed one > > http://wiki.openstreetmap.org/index.php/Proposed_features/smooth Great, I'll have a look later on. > >> Also, are there are examples where it does work well and where it >> doesn't? > > I see two problematic cases with this approach : assuming you have > one flowing road that you've split up in multiple ways for > whatever reason. Now there could be a tangential discontinuity > at the junction point. I feel this is more a theoretical problem. > In practice people will probably put two > extra nodes close to the junction point to 'guide' the tangential > direction at both ends if the break is visually disturbing. > > The other case is related : assuming a flowing road with one > sharp corner. Whereas now you just lay it out as one way, you might > want to split this road to preserve the sharp corner in my proposal. > > Not a big deal either : in the worst case you can still fall back > to an ordinary way and just add a bootload of points to make it > appear smooth as we do now. Sounds good to me. Artem > > cu bart > > _______________________________________________ > dev mailing list > dev@openstreetmap.org > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev _______________________________________________ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
