[mkgmap-dev] [mkgmap-svn] Commit r572: MDR16 is some kind of codebook.

Sat Dec 18 11:10:20 GMT 2021

Hi Ticker,

maybe the table allows to decode the strings faster or someone very
unexperienced invented the code or it's intended obfuscation or
Garmin took an algo that was meant for something else and what we
see is partly ignored.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Samstag, 18. Dezember 2021 11:52
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev]       [mkgmap-svn]    Commit  r572:   MDR16   is      some    kind    of      codebook.

Hi Gerd

I'm amazed at how they've made something that could be simple and
expressed with a few byte of control, around 140 bits for tree
structure and 80 or so bytes of characters so big and complex!

Maybe the few (5) layers closest to the root somehow hard coded.

Where a node has a sub-tree on one side and a letter on the other, are
these always the same way round, such that the these will always tend
to one side of the tree, with nothing beyond because of double leaves
closer to the root stop the tree. This would allow reasonable length
bit sequences to describe the structure at each level, rather than it
growing by powers of 2.

Ticker

On Sat, 2021-12-18 at 10:19 +0000, Gerd Petermann wrote:
> Hi Ticker,
>
> sorry, my last post turned out to be wrong. The byte at offset 2 must
> have a different meaning.
> The previously posted mdr16 for benelux has a value of 2 but 4 bytes
> for the "struct",
> while the hungary map has a value of 2 and only 3 bytes for struct.
> Maybe the value for
> 3 / 4 can be calculated from the depth of the tree.
>
> I still have no idea what the values mean. I thought of some kind of
> raster image or a jump table but
> nothing worked out so far..
>
> Gerd

_______________________________________________
mkgmap-dev mailing list
mkgmap-dev at lists.mkgmap.org.uk
https://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev