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

Wed Dec 15 18:26:00 GMT 2021

Hi Gerd

This could just be the way the tree has been flattened, with the data
for longest sequences at the end, just happening to be byte aligned and
without intervening bit markers to represent the tree because they have
occurred already.

regarding the 00000000000000s, maybe this a an escape followed by a
fixed length index into Mdr 30/31 or whatever, and, as only 1 entry, it
is zero, if there were more it could be 0000000000{fixedLenInxNotZero}

Ticker

On Wed, 2021-12-15 at 17:35 +0000, Gerd Petermann wrote:
> Hii Ticker,
> 
> reg. MDR16: When I print the encoded characters which require 8 or
> more bits in the order of the Huffman tree
> they build a sequence which appears at the end of MDR 16 (last 60
> bytes or so).
> Those chars which are encoded with fewer bits are still a mistery to
> me.
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Gerd Petermann <gpetermann_muenchen at hotmail.com>
> Gesendet: Mittwoch, 15. Dezember 2021 13:07
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev]       [mkgmap-svn]    Commit  r572:  
> MDR16   is      some    kind    of      codebook.
> 
> Hi Ticker,
> 
> it's almost impossible to guess when there is only one entry in MDR
> 30/31 and only one occurence of the code
> "00000000000000000000".
> I used '#' in my debug code to mark an "unknown" char.
> 
> A possible meaning could be that 30/31 are common prefixes and 32/33
> are common suffixes in road names.
> I doubt that this is related to the Huffman encoding. Maybe the code
> "00000000000000000000"
> simply represents a special character that is replaced with a
> corresponding string in 30/31?
> 
> No idea how that would work with the suffixes.
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Ticker Berkin <ticker at jagIT.co.uk>
> Gesendet: Mittwoch, 15. Dezember 2021 12:47
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] [mkgmap-svn]  Commit  r572:   MDR16  
> is      some    kind    of      codebook.
> 
> Hi Gerd
> 
> Do you think there might be some form of escape sequence that is
> followed by a ref to the clear road names in Mdr 30..33. I noticed
> when
> looking at MapInstall manipulated Mdr that the '#' sort got changed.
> 
> Ticker
> 
> On Wed, 2021-12-15 at 11:13 +0000, Gerd Petermann wrote:
> > Hi Ticker,
> > 
> > this is what I have so far. The non-printable characters 0x01..0x04
> > are probably not correct.
> > Note the special case with the last sequence. It only occurs once
> > in
> > the
> > index and may as well be an error in the data.
> > My code doesn't detect any unknown codes, so I think MDR16 must
> > somehow contain this information.
> > The character ž seems to appear both in upper and lower case?!?
> > Might
> > be wrong.
> 
> 
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