[OSM-dev] Binary tiling scheme

jamesmikedupont at googlemail.com jamesmikedupont at googlemail.com
Wed Sep 1 05:46:57 BST 2010


Hi,
my only spontaneous thought is this :
what if we can add in a zoom level to the tiling, so that map elements
visible at zoom level 1 are in one tile, and less visible elements are
stored in a sub tile? basically any tile will contain only elements at
a certain level of zoom.

additional constraint, the tiles will all fit into the existing tiling scheme,

with those two constraints, you will be able to render each tile at
each zoom level with an efficient memory and cache profile.
mike

On Sun, Aug 29, 2010 at 5:14 PM, Frank Steggink <steggink at steggink.org> wrote:
> 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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>



-- 
James Michael DuPont
Member of Free Libre Open Source Software Kosova and Albania
flossk.org flossal.org



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