[mkgmap-dev] r4015 in dem-tdb branch implements --x-overview-dem-dist

Fri Dec 22 16:11:34 GMT 2017

Hi,

okay, so we now have three new (still undocumented options) to enable hillshading and calculation of elevation data in routes.
Here is a summary of the new options:

--x-dem=path_to_dir[,path_to_other_dir,...]
gives one or more directories containing *.hgt files.
--x-dem-dists=n1,n2,n3,...
Sample from a Garmin Demo map: --x-dem-dists="5520, 16560, 44176, 88368" 
should contain one number for each level in case you want to use the DEM data in a gmapsupp, the values give 
the number of DEM units between two points. A DEM unit is 360° / 2 ^32.
The higher the numbers the smaller the DEM file. Useful values for level 0 start
at 1600 if you have 1'' hgt data and a small area, for large areas consider to use 8000 or more. If this option is missing mkgmap will calculate one DEM 
level based on the resolution of the hgt files.
--x-overview-dem-dist=n
Use this option to add DEM also to the overview map. The value again gives the distance between two DEM points.
It the option is not given or the value is 0 the creation of DEM data for the overview map is disabled. This might be needed for large areas and for overview img files which
are already close to 16MB .
Useful are probably values > 100000, e.g. 256000

Expect to see "There is not enough room in a single garmin map for all the input data. The .osm file should be split into smaller pieces first."
when experimenting with these options. The additional amount of bytes for the DEM files depend on the above options, and the relief of the area. Mountains 
require much more space compared to flat areas like the netherlands.
If you have contour lines in your overview map try without.

I'll try to add code to splitter so that it creates smaller tiles for areas with many mountains. I don't know yet how to store that info.

Gerd