[OSM-dev] Binary tiling scheme

Frank Steggink steggink at steggink.org
Sun Aug 29 16:14:06 BST 2010


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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