On 26.03.2011 13:11, Charlie Ferrero wrote:
On 26/03/2011 15:50, Johann Gail wrote:
Actually, we do have a mean: if there are multiple parallel tracks (each
drawn as a separate way with railway=*), it is a major railway. It should be doable to merge adjacent ways at lower resolutions and sum the "weights" of the ways, to decide what to draw. A style file extension could be useful, to specify e.g., the following:
* draw individual railways at resolution 24 * merge parallel tracks to one and draw them at resolution 22..23 * merge parallel tracks to one and draw if count>1 at resolution 21 * merge parallel tracks to one and draw if count>3 at resolution 20
For polygons, it could be useful to specify the minimum size that qualifies for inclusion in a given resolution. Of course, small adjacent polygons would have to be merged together first.
I am beginning to think that it could be useful to have low-resolution versions of the OpenStreetMap data, generated by an experimental algorithm that attempts to merge polygons and lines as suggested above. If it is not too CPU intensive to merge adjacent areas and lines, perhaps it could be implemented inside mkgmap after all.
I'm thinking since some time about an algorithm for merging small polygons. Up to now I have not found an suitable algorithm. In another case I have thought about merging parallel lines, especially the both tracks of highways. While reading your mail I got the insight, that this are possibly two similar problems. In both cases there should be two objects with a small space between it be replaced by a merged single one.
The algorithm in general would be: - Increase all polygons/lines with a outline. - Check all increased polygons, if some of them overlap. - If so, merge the original version of them.
But I expect this to be a really resource hungry task.
Regards, Johann.
I thought the --merge-lines option did part of what you're saying? i.e. merge lines at low zoom levels. If it doesn't do that, then what does --merge-lines do?
it merges a single street consisting of several parts (behind not beside each other) into one street if name is equal (more or less).