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[mkgmap-dev] Embedding raster maps

From Oliver Eichler oliver.eichler at gmx.de on Mon Jan 4 13:07:38 GMT 2021

Hi Steve,

I tested your map. It's not listed either. I have a GPSMap64s and placed it into the internal as well as into the external memory.

I removed all other maps on the device, except the basemap. The basemap is the only one listed.

I made a minimum test.img, too. It contains no points, lines or areas. It has 3 zoom levels 22..24 with a sub-division each. I also uploaded a log from my test decoder.


I uploaded a second one with the version in the header set to 2. So far the difference to be another offset for the FAT.

Maybe you can cross check if your device is willing to list them.



> Gesendet: Sonntag, 03. Januar 2021 um 23:08 Uhr
> Von: "Steve Ratcliffe" <steve at parabola.me.uk>
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: Re: [mkgmap-dev] Embedding raster maps
> 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:
>    http://files.mkgmap.org.uk/download/494/gmapsupp.img
> (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
> empty)
> 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.
> Cheers,
> Steve
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