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[mkgmap-dev] what do the 0x4a polygon in the mean?

From Gerd Petermann gpetermann_muenchen at hotmail.com on Sun Jan 14 09:49:35 GMT 2018

Hi Andrzej,

thanks for the hints.
It seems indeed to be an alternative to use a very large overview-dem-dist value in combination with no DEM data.
Garmin uses this in the "Winterkarte" and in the Adria Map.
Also, the overview map of "Winterkarte" is the first map that I found in which dem-dist for lat and lon ar different:
map units between points (latitude): 86517760
map units between points (longitude): 205701120

Maybe I change meaning of option --overview-dem-dist=0 to produce this special small DEM file instead of no DEM.


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej at poczta.onet.pl>
Gesendet: Samstag, 13. Januar 2018 17:24:35
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] what do the 0x4a polygon in the mean?

Hi Gerd,

 > 1) don't add DEM to overview map (a work around)

Maybe it would work, but I remember getting problems with overview
without DEM (I forgot what it was, maybe even not because of DEM?). I
think it would be better to add what I call "empty DEM" instead.

The empty DEM layer contains 4 bytes of data: 0 0 0 2
Header of a layer is the same, tiles are 64*64, but there is no tiles,
only extra rows and columns. Word defining structure (recordDesc) is
0x10 00. Number of rows and columns is small, like for example 4, and
distance between points is big.

You can see this in Adria Topo. There is update here, which can be
installed on PC (including Mapsource):

Link to map doesn't work because of redirections, but you can extract
final address from link and download map. You can even browse map in
Mapsource, if you provide unlock key: DEMO

 > 2) use a slightly smaller polygon

This is other solution of Garmin, but they use bigger polygon in
overview, increased by about 700m outside. So jaggies are far from map

 > 3) Find a flag or something else that tells the PC program that it
should stop rendering the overview DEM at some level.

I doubt it is possible.

Best regards,
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mkgmap-dev at lists.mkgmap.org.uk

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