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[mkgmap-dev] Embedding raster maps

From Gerd Petermann gpetermann_muenchen at hotmail.com on Tue Jan 25 08:10:47 GMT 2022

Hi Steve,

if I got that right data in RGN5 is like MDR16, means, it contains Huffman decoding data. At least a lot of bytes look similar
and GPXSee also gets the decoding data from it.

Most of the code that displays MDR16 can be used to read RGN5, too.


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Steve Ratcliffe <steve at parabola.me.uk>
Gesendet: Donnerstag, 7. Januar 2021 11:31
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] Embedding raster maps

Hi Oliver

 > 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.

To be clear, nothing is visible on my device either with that
polygon type.
Only if I change the type to something else (I used 0x10101) do I see
anything.  As far as I know extended polygons work in mkgmap and
I just assumed that it is a reserved type for the images or something

 > 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.

mkgmap sets all of these to zero and seems to work.  Of course it may
not work for your purpose with the images.  I would try taking a
copy of a working map and zeroing out some of the unknown things
until it stops working. You will then know if something is essential
or not.

I have no ideas about what byte0x00000025_0x00000038 could be.  They
look like bitmaps or flags to me.

 > Maybe one of you has an idea what it's about. I also uploaded my

I've had a go at displaying this section and I have uploaded
a sample to:

There is an initial part followed by two lists, the first has
five byte records and the second 4 bytes.  My guess is that
the first one is related to polygon types and the second
is some kind of index sorted by type or by zoom and/or division.

Presumably it points into the extended polygon section, but I do not
have anything that displays that section at the moment so I can't
yet match anything up.

The code I used is in the method RngDisplay::displayRgn5() in the
display project.
(The particular file is at
This works with the files that are available to me, maybe not on
anything else :)

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