[OSM-talk] tiles at home optimizations

[Dirk-Lüder Kreie]

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Hi to all you renderers

Inspired by OJW's TilesPipe script I've come up with an idea about how
to significantly improve the rendering without the projection issues
associated with cutting up a bigger tile.
The new tilesGen.pl is in svn, along with the old version now called
tilesGen_noGD.pl (no GD because the new version requires the perl GD
library)

Details:
when cutting up a larger Region north to south brings problems with
the projection if it is done symmetrically (i.e. cutting up a
8192x8192 px bitmap in equal 256x256 px tiles). However just cutting
from east to west doesn't create those issues. So instead of calling
inkscape for each individual tile and subtile the new version renders
the lvl 12 tile, and if that's not empty it renders stripes of the
higher zoom tilesets:
Two 512x256 stripes for zoom 13, four 1024x256 stripes for zoom 14 to
32 8192x256 stripes for zoom 17 that are subsequently cut up into
individual 256x256 px tiles identical to those rendered by the old
version, thus reducing the amount of inkscape calls to 63 instead of
up to 1365 for a tile that has data in every z16 subtile.

Result: My 5 renderers combined can now render tiles faster than I can
compress and upload on a 384 kbit upload DSL line.

Have fun :)

Dirk-Lüder "Deelkar" Kreie

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