On May 27, 2011, at 10:33 AM, Flo Ledermann wrote: > Hi Dane, > > On 05/25/2011 10:12 PM, Dane Springmeyer wrote: >> re: contributing to the wiki - I would love help. I figured >> adding/refactoring this page would be the place to start: >> >> http://trac.mapnik.org/wiki/Troubleshooting > > Funny that you point me to that page, because the issue described on > that page was another one I was running into (polygons across the > dateline).
Common story with Natural Earth - rich data but understandably not perfect for reprojection. > But in my case I tried to use the +pm parameter of the PROJ.4 > projection string to "rotate" the earth to a different center meridian > on purpose. You are a proj4 wizard I see :) > > In this case neither clipping nor the +over parameter would help me, > because with the first I would loose the geometry "coming out" on the > other side, while with the second the whole projection would just be > shifted and I would end up with a distorted projection that still has > good ol' Greenwich at the center. Ya, I would recommend clipping the data rather than using proj4 to adapt. > > I once wrote a simple map renderer in Java where I included a heuristic > algorithm to split "wrapping" polygons in two on the fly while rendering > -- detect the dateline crossover in the polygon's vertices, and in case > it happens create a second polygon on the fly and assign subsequent > vertices to it until it crosses back again. > > Would you be in favour of such a feature ever being introduced in > Mapnik? If clipping the data ahead of time fixes your problem, that seems like the best recommended route. If not, then let's discuss more. > I am not sure what the performance implications for the 99.9% of > the cases that don't need that feature would be (I guess it should only > be an optional rendering mode activated by a flag or something). If > there are no fundamental objections against it, I could try to reproduce > what I did in Java in the C++ code (given my coding skills are sufficient) > > Regarding the wiki, are you distinguishing between Mapnik and Mapnik2 > (as there are maybe different solutions available, or even different > problems), or is this just a temporary distinction? Use your best judgement - thanks! > > Best, > > Flo > _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
