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. 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) 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. > 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 > 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. cu bart _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
