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[mkgmap-dev] Tile names in IMG files

From Steve Hosgood steve at tallyho.bc.nu on Fri Sep 4 16:26:32 BST 2009

Steve Ratcliffe wrote:
> Hi
> On 04/09/09 10:16, Steve Hosgood wrote:
>> "I<hex number>.GMP". Does anyone know how the<hex number>  is derived
>> please? I guess that it is a bit-interleave of the latitude and
>> longitude of some reference-point in the tile, but it could be a
>> byte-interleave, or a nybble-interleave, or the interleave is done with
>> the number expressed in decimal or whatever.
> I don't think there is any big significance to the names, they
> can be fairly arbitrary strings.
Ah - not so! The .MDR file (not yet created by mkgmap) stores the names 
of subtile-files as 32-bit integers and expects the subtile files 
themselves to have names of the 'printf' format "I%07lX.GMP". See 

There is a rumour on that wiki page that the subtile files can also be 
of a 'printf' format something like "%08ld.GMP", but I've not personally 
see that.


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