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[mkgmap-dev] Embedding raster maps

From Steve Ratcliffe steve at parabola.me.uk on Sun Jan 3 22:08:59 GMT 2021

Hi Oliver

 > What is the minimum data an IMG file has to contain to be listed
 > on the device?

Its an interesting question. I don't remember having too many problems
getting a map recognised in the beginning.  At r20 it worked
according to the commit comment but I only added the test map
builder at r24.

However on my etrex 30 the map produced by r24 does not work.

The first one that does work is r79.  With a bit of experimenting
I discovered that adding a sufficiently large gap between the
end of the TRE header and the first data would make r78 work too.

Going back to r24 and adding more padding also produced a map that
was recognized.  I was able to remove the second copyright message
too and all map data.

The required gap was between 40 and 101, depending on the rest of
the code.

So this all makes very little sense and it is possible that this is
covering for something else that we don't understand.

I've uploaded the minimal IMG file at:

(After this I also managed to remove the first copyright message, so
you do not need any copyright messages and the label section can be

With this version there is no message displayed on startup, which is
something that was fixed in r79 I think.

There is just a single zoom and subdivision in the TRE section and
no points, line or polygons.


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