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[mkgmap-dev] r4033: new dem options are now documented

From Gerd Petermann GPetermann_muenchen at hotmail.com on Sat Jan 6 11:09:39 GMT 2018

Hi all,

see http://www.mkgmap.org.uk/doc/options
I've added them in a chapter headed "Hill Shading (DEM) options"
This also means that you no longer need the --x- prefix when using r4033 or newer.

Please suggest improvements, esp. if you have found rules to determine "good" dem-dists values.
If possible I'd like to do the calculations in mkgmap instead of asking each user to find out what is good.
Maybe option --dem should be changed to --dem-source before merging to trunk?

I think these are the other open problems now (no particular order):
-- determine optimal block-size to avoid MapFailedExeption with large DEM files, if that is too complex we'll change the default from 512 to 2048.
-- find possible encoding error for low resolutions, esp. in overview maps. Frank Stinner tries to find a solution for this :-)
-- Problems with java heap when creating large or highly detailed maps:
Zipped files require more heap memory because the current implementation has to keep a copy of the unzipped content while unzipped files
are kept in MappedByteBuffers which don't require java heap. On the other hand they maybe cause other problems as those reported by Carlos:
One work around would be to keep the unzipped data in temporary files (more I/O), another solution might be to further change the algorithm
so that it doesn't require full random access to all(!) hgt files "touched" by the overview map. I've already tried to change that with r4027
so that only some rows are required, but that code is not very elegant. I hope I find a better solution for this. 
@Frank: I think BuildDEMFile also has this problem, right?
-- The code needs further clean up , javadoc and unit tests. 

Thanks for the good feedback so far, I think this will be another big improvement if merged into trunk.


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