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

[80n]

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.

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?

The problem is easy to see here:
http://www.informationfreeway.org/?lat=50.917162525157984&lon=0.5942957037543497&user=80n&zoom=7&layers=B000F000T
The caption layer is showing Brighton, for example, about 50 miles north of
its real position.

Does anyone have any ideas?

80n
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