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[mkgmap-dev] splitter, mapid

From Gerd Petermann gpetermann_muenchen at hotmail.com on Thu Jan 3 07:20:01 GMT 2019

Hi Andrzej,

looked at this again now. What I don't understand is why you want to use
exactly the same formular
as Garmin. I think my approach would be to make sure that we DON'T use their
numbers to avoid conflicts.


popej wrote
> 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
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> mkgmap-dev at .org

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