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[mkgmap-dev] Issues generating DEM

From Andrzej Popowski popej at poczta.onet.pl on Sat Nov 25 15:34:37 GMT 2017

Hi Frank,

I have successfully build several maps with DEM, thanks again for your tool.

I have tripped on out-of-memory problems too. One case is, when tile is 
too big. This I can deal with, simply preparing smaller tiles. I think 
the limit is about 200 degree square.

Other problem is with preview maps. I can't make it smaller. What I can 
do is to make hgt files smaller, since there is no need for full 
resolution for preview. Unfortunately your program assumes, that dummy 
tile is always 1201x1201. So regardless of hgt size, memory is full 
anyway, since my preview maps include a lot of sea.

Side note: isn't predefined size of dummy tile an error? What does 
happen, when I use 1-second hgt with size 3601x3601? It has worked for 
me, but maybe I was lucky? But if it works, then maybe use 3x3 size for 

I have recompiled BuildDEMFile, adding option for hgt line length 
(actually I have reused usedummydata for this purpose). So now I can use 
hgt files downsized to 76x76. This allow me to create very big preview 
maps, like for a full continent.

I think BuildDEMFile could downsize hgt files on the fly, when there is 
big difference in DEM pixel size compared to hgt pixel. I hope you could 
consider addition of that kind of functionality.

Best regards,

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