[OSM-dev] [Tilesathome] Projection problem with tilesgen.pl at very low zoom levels

[80n]

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 <kleptog at gmail.com> wrote:

> On Jan 21, 2008 11:58 AM, 80n <80n80n at gmail.com> 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 <kleptog at gmail.com> http://svana.org/kleptog/
>
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