[mkgmap-dev] different DEM file sizes from mkgmap and BuildDEMFile

Thu Dec 21 17:25:58 GMT 2017

Hi all,

I've noticed that BuildDEMFile typically writes larger DEM files.
One reason is that a missing hgt file is not treated as sea (where all heights are 0),
instead --usedummyvalue seems to mean "treat as invalid". 
In the past, some hgt files contained such holes with invalid values, but I think 
nowadays better files are available.

I've also noticed that the two programs sometimes interpolate slightly 
different value. I did not yet check which one is better. 
I plan to add a some unit tests to find out.

Gerd