On 05/10/10 17:26, Csongor Nemes wrote:
Our product, OpenMaps (currently available on the iPhone and the iPod touch), is the only one which lets you tap on POIs on the map. We use the default OSM map as the default map type in our app, but the user can change to OpenCycleMap and OpenPisteMap as well; also the user can add custom map types (e.g. OSM Osmarender). We need to know the exact location of the symbol inside an area (currently we use an algorithm which doesn't always match the rendered symbol's location). The best solution (from our perspective) would be to request the calculated center from OSM, but I'm not sure that it's possible. Otherwise we will implement the algorithm. If I'm not mistaken slightly different algorithms are implemented in different renderers. We are interested in the Mapnik version for now. Point me in the right direction, please; where can I find a description of the algorithm and which source files contain the implementation?
You'd be better off asking on the mapnik-dev list but I believe that the calculation comes from geos and is a very simple centre-of-mass type calculation.
Note that there was some discussion at the recent mapnik code sprint of making this more intelligent, so I wouldn't count on it staying the same. Equally it is quite likely that at some point mapnik may get the ability to move the icon/label around a bit to try and find free space - if that happens then there won't be the sort of algorithm that you're looking for at all.
Tom -- Tom Hughes (t...@compton.nu) http://compton.nu/ _______________________________________________ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
