[mkgmap-dev] splitter, mapid

Tue Dec 18 13:14:08 GMT 2018

Hi Gerd,

yes, I got the formula after examining numerous Garmin's maps. I know, 
that City Navigator is different, my guess is that next CN map gets next 
free mapid. I'm not sure about marine maps and other new maps from Garmin.

It looks like the formula is easy to support up to FID 45744. For bigger 
values you could take different strategy. The rules I know are following:

Mapid inside img data is 4-byte value, no problem here.

File names are independent of mapid, could be any arbitrary 8-digit 
number (number from file name could be even written in TRE header, at 
offset 0xCF).

Names of subfiles like 12345678.TRE can be written in HEX, in this case 
you should use prefix 'I'. So 12345678.TRE is equivalent of 
I0BC614E.TRE. Mapid 140.531.712 could correspond to I8605800.TRE.

My first suggestion is to limit --fid to max 45744. For bigger FID 
option --mapid should be used.

Second proposition is to overlap mapid values for big FIDs, but with an 
offset of 1024. So for FID > 45744 formula could be like this:

mapid = (fid - 19792)*2048 + 6316032 + 1024

-- 
Best regards,
Andrzej