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?
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.
I guess mkgmap must generate tiles too, so this info is likely well-known to those involved in the code.
We just use digit only names and the number is assigned by the mapmaker, or the tool they use to split the map. ..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?
Yes that is what mkgmap does. I don't think it makes any difference to anything else.
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 http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/MDR_Subfile_Format#MDR1... 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. Steve
Hi On 04/09/09 16:26, Steve Hosgood wrote:
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 http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/MDR_Subfile_Format#MDR1...
Well I don't agree. If you go to http://mapcenter2.cgpsmapper.com/ and download any of the freely available maps from there, you will see many (probably all of them) that have names that are 8 digits. It appears that all of the ones that have an installer have a mdr file. A map has a name and a number. We always make the name to be the string representation of the number, as I believe does cgpsmapper. It has never caused a problem before. ..Steve
Hi, On Fri, Sep 04, 2009 at 04:26:32PM +0100, Steve Hosgood wrote: [...]
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 http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/MDR_Subfile_Format#MDR1...
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.
NT maps: "I%07lX.GMP" --> NT maps classic maps: "%08ld." + ("TRE", "RGN", "LBL", ...) My guess on this... Elrond
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Elrond -
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Steve Ratcliffe