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[mkgmap-dev] Embedding raster maps

From Oliver Eichler oliver.eichler at gmx.de on Wed Jan 6 10:36:54 GMT 2021

Hi Steve,

thanks for the file. On my device nothing is visible at all. But that's kind of an information, too. There is no way to circle down bugs by simply skipping the extended part.

Probably it is still some missing encoding. In the Isle of Man map (and others) there is much more information in the RGN header. Note the values in the "filling bytes". And there seems to be an additional section after the extended point2 section. I called it offset1/length2.

   --- RGN header ---
                          size 007D
                          type 47 41 52 4D 49 4E 20 52 47 4E | GARMIN RGN
                byte0x0000000C 01
                          flag 00
                          year 2010
                         month 7
                           day 21
                          hour 9
                        minute 53
                        second 6
                       offset1 0000D54E
                       length1 00000000
                 offset_polyg2 0000D54E
                 length_polyg2 00001A1F
     byte0x00000025_0x00000038 02 00 00 00 00 00 00 00 FF 00 00 20 FD FC 03 00 00 00 00 00 
                 offset_polyl2 0000EF6D
                 length_polyl2 00000000
     byte0x00000041_0x00000054 00 00 00 00 00 00 00 00 3F 00 00 20 FD 0F 00 00 00 00 00 00 
                 offset_point2 0000EF6D
                 length_point2 00000000
     byte0x0000005D_0x00000070 00 00 00 00 00 00 00 00 FF 07 00 20 3F F7 3F 00 00 00 00 00 
                       offset2 0000EF6D
                       length2 0000020B
                       unknown 000000E3

This section has a variable length in different sub-files. The unknown value E3 can be E5, too. It doesn't seem to be a record size. 

I had a look at several sections. They are not completely random, thus there seem to be no "compression". However the patterns do not ring a bell for me. I copied a couple of them into a file and loaded it into my cloud share:


Maybe one of you has an idea what it's about. I also uploaded my current version of the test map with a single raster map tile. It does not show. Top left coordinate is N46° 57.768 E011° 47.484.

Sadly I am stuck here and I am running out of quality time to concentrate on the topic. 

I also have to update QMapShack's decoding. While reading the mkgmap source code I noticed a lot of new stuff that is not covered by the decoder.



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