[mkgmap-dev] DEM format Questions

Wed Nov 15 12:22:41 GMT 2017

Hi Gerd,

at first the good news. In the meantime i have build maps for Czech 
Republik, Germany, Austria, Switzerland and Italy, ever with 6 zoomlevels. 
I don't found an error. Of course, this is no evidence for the algorithm.

And yes, there are a few mysterious things. I'm sure, what ever the garmin 
programmers done, they have found a very good compression for this special 
case. They don't waste a bit. But perhaps they think also to confuse all 
the snoopy guys on the world. Perhaps they say: hey let us take a special 
case, if the compression is not worse.

I have no idea for the 158. I belief, we can see this as parameter. 
Perhaps garmin have found with trial and error, that 158 give smallest 
DEM's for a lot of areas on earth. Then it is more a "statistical" reason.

By the way, the worst thing in my opinion is the rule for 
"Längencodierung". It is rather a "descriptiv" solution. Perhaps behind 
this is a more "mathematical theory", but i don't found it.

Frank
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