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[mkgmap-dev] splitter, mapid

From Gerd Petermann gpetermann_muenchen at hotmail.com on Tue Dec 18 05:42:13 GMT 2018

Hi Andrzej,

thanks for that formula. I like the idea to use the fid as option for splitter.
I'm not yet sure if I understand. Up to now we use values for mapid that are up to 99.999.999 so that the tile names can use the number.
Presuming that fid can be any value up to 65535 we get 2048 * 65535 + 6316032 = 140.531.712. Should splitter change to hex in this case, e.g. 08605800.osm?
Can you explain the odd number 6316032? Did you find it by looking at the numbers used in Garmin maps?


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej at poczta.onet.pl>
Gesendet: Montag, 17. Dezember 2018 15:17
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] splitter, mapid


basically map ID should be unique for all tiles, regardless of FID. If
you load 2 tiles with the same map ID to a GPS, it will silently ignore
one of these tiles. Most probably GPS assume, that these are the same
tiles and there is no reason to process both.

Search index contains map ID. If you use 2 maps with repeated map ID,
then most probably search won't work correctly.

There is no problem with map ID in Basecamp or Mapsource, these programs
don't support multiple maps.

I suggest to link map ID with FID using following formula:

First map ID in a mapset = FID*2048 + 6316032

Or in hex:
First map ID in a mapset = FID*800h + 606000h

This formula assigns 2048 IDs for each FID. It should be true also for
original Garmin's maps, except for City Navigator series.

Gerd, maybe you could include these formula into splitter? Something like:
:  Calculate mapid basing on a FID value. Can be used instead of
--mapid. Splitter sets first mapid value as 2048*fid + 6316032

Best regards,
mkgmap-dev mailing list
mkgmap-dev at lists.mkgmap.org.uk

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