Martijn Thanks, I think I've got a handle on the probable cause now. Not sure yet what the best solution is.
The South Africa issue appears unrelated - its more likely that two adjacent tiles were generated with different versions of something. The latitudes should otherwise match across tiles. 80n On Jan 21, 2008 11:40 AM, Martijn van Oosterhout <[EMAIL PROTECTED]> wrote: > On Jan 21, 2008 11:58 AM, 80n <[EMAIL PROTECTED]> wrote: > > I've been working on a captions layer for low zoom levels (z4 - z7). > > > > The results are nice, but there seems to be a projection problem. Items > are > > being displaced vertically. > > > > Everything is spot-on for z8-z12, but when I try to repeat the process > for > > z4-z7 then the error is apparent. > > > > I'm guessing at the moment that the problem has always been there, but > is > > insignificant at z8, whereas at lower zoom levels it starts to become > quite > > noticeable. > > Sounds a lot like: > http://wiki.openstreetmap.org/index.php/Osmarender_bug > > The error grows by the square of the zoom, so at lower zoom levels it > gets worse, much worse. > > > Is there anyone who is familiar with the mercator projection code in > > tilesgen.pl / tahproject.pm that might be able to shed some light on > this > > problem? > > My guess is that the mercator preprocessor needs to be invoked to > project each point individually, and not just the four corners with > linear interpolation. > > Note: I think the new lowzoom process has similar issues: > > http://www.informationfreeway.org/?lat=-33.92&lon=22.52&zoom=11&layers=B000F000F > > Have a nice day, > -- > Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ >
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