[mkgmap-dev] DEM format is better than zip

Wed Jan 10 15:05:42 GMT 2018

Hi all,

FYI:
Today I've coded a quick+dirty solution to use Garmins DEM format to compress hgt files.
The compression ratio is much better than that of zip, on average the file is < 50% of the zip file, and the format should allow nearly random access,
so maybe it would be the better input for mkgmap.

I've also compared with bzip2 (with -9 = highest compression), file sizes are similar to DEM.
I've not coded the decompressor, but I've used DemDisplay to verify that it works in principle. 
Complete code to compress + decompress would take some days.

I see no real use case for this at the moment, just wanted to let you know. 

Gerd