[mkgmap-dev] Tile names in IMG files

Fri Sep 4 10:16:17 BST 2009

Folks:
Inside official Garmin IMG files there are typically several tiles named 
"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 guess mkgmap must generate tiles too, so this info is likely 
well-known to those involved in the code.

Thanks in advance
Steve

BTW: I gather that is possible for subtile files to be given 
decimal-based filenames too. How does that work? Is there any difference 
in the actual files depending on the naming system used?