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[mkgmap-dev] r4006: 1st alpha version to write DEM data

From Gerd Petermann gpetermann_muenchen at hotmail.com on Tue Dec 19 18:16:13 GMT 2017

Hi Nick,

thanks for reporting. Yes, I saw a similar issue with a horizontal line at 47° / 48° today and I think I fixed it. Seems that I have to do
something different for vertical boundaries.


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von osm at pinns <osm at pinns.co.uk>
Gesendet: Dienstag, 19. Dezember 2017 19:12:57
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] r4006: 1st alpha version to write DEM data

Congratulations Gerd! Brilliant.

I know its just the beginning.

Have just done Luxembourg - very fast - however there is an obvious dip perhaps where 2 hgt files join?




On 19/12/2017 17:41, Gerd Petermann wrote:

Hi all,

r4006 in the dem-tdb branch implements a new option

It will crash if any hgt file is missing, probably there are also other stupid problems, e.g. with negative lat/lon values.

It cannot (yet) read zip files, so the directory must contain unzipped *.hgt files.
The hgt files can be in 3'' or 1'' resolution, but for now DEM data is always stored with 3'' res.
I plan to change that soon, so that 1'' is used if at least a part of the tile is covered by 1'' SRTM data.

It doesn't yet create DEM for the overview map and it only creates DEM for level 0.
So far I've only implemented a very basic hgt reader which doesn't do any interpolation,
this might change soon.
I did not check if the flags in the tdb file are set correctly now, I've only created some small
maps for parts of the alps so far and they looked good in Basecamp /Mapsource.

If you want to try this version, see

My currennt understanding is that mkgmap should do the calculation of the DEM resolution based on the
levels used to create the rest of the map. I have to find out how to calculate the values for lower resolutions.
I assume it has to be the average of the values, so if at res 24 we have 4 points with 123, 124,128, and 122
the value for res 23 would be Math.round((123+124+128+122)/4) = 124. For res 22 it would be the average of 4*4=16 values,
and so on. Does that make sense?

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