Hi,
I have created a tiling scheme which is based on division in two parts
of a parent cell, alternating in the x and y directions. It can be used
to chop up a rectangular area, so that each resulting tile contains less
data than a certain threshold. I've devised it as a possible answer to
the problem that some of Computerteddy's IMG files, particular in the
Netherlands, can't be generated due to their size.
This binary scheme is in contrast to the quad tiling scheme which is
often used (like in Google Maps, or the CanVec import tiles), where each
division ends up in four cells. However, when a quad scheme is used,
you'll end up with more redundant tiles, of which the combination does
not exceed the threshold either.
Another benefit of this binary division is that each subtile can be
identified by a unique integer value. This can be very convenient. It
also means that the location of the subtile within the base tile, as
well as its size, are implicitly stored. This scheme is also not limited
by scale.
When a parent tile has number n, its children will have the numbers 2*n
and 2*n+1. If you're familiar with genealogy, this is the same as the
Ahnentafel numbering (Sosa-Stradonitz). However, where as in genealogy a
child has two parents, this is completely the opposite here. (A parent
tile can be divided into two child tiles.)
More information can be found on the OSM wiki: [1]. If you think it is
useful, please let me know.
Regards,
Frank
[1] http://wiki.openstreetmap.org/wiki/Binary_tiling_scheme
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