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

Tue Dec 19 17:41:04 GMT 2017

Hi all,

FYI: 
r4006 in the dem-tdb branch implements a new option
--x-dem=path_to_dir_with_hgt_files

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 
http://www.mkgmap.org.uk/download/mkgmap-dem-tdb-r4006.zip

@Frank:
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?

ciao,
Gerd