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

Sat Jan 6 19:02:40 GMT 2018

> Date: Sat, 6 Jan 2018 16:51:43 +0000
> From: Gerd Petermann <gpetermann_muenchen at hotmail.com>
> To: Development list for mkgmap <mkgmap-dev at lists.mkgmap.org.uk>
> Subject: Re: [mkgmap-dev] r4033: new dem options are now documented
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> Hi Mark,
>
> my understanding is that files with version 2.1 have many voids. You find them here:
> https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/
> The files from here seem to have few voids : http://viewfinderpanoramas.org/dem3.html
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von EthnicFood IsGreat <ethnicfoodisgreat at gmail.com>
> Gesendet: Samstag, 6. Januar 2018 17:42:41
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: Re: [mkgmap-dev] r4033: new dem options are now documented
>
>
>> Date: Sat, 6 Jan 2018 11:09:39 +0000
>> From: Gerd Petermann <GPetermann_muenchen at hotmail.com>
>> To: "mkgmap-dev at lists.mkgmap.org.uk" <mkgmap-dev at lists.mkgmap.org.uk>
>> Subject: [mkgmap-dev] r4033: new dem options are now documented
>>
>> 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:
>> http://gis.19327.n8.nabble.com/mkgmap-r4025-implements-x-dem-poly-option-tp5909038p5909257.html
>> 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.
>>
>> Gerd
>>
>> ------------------------------
> Thanks for the documentation Gerd.  I look forward to creating my first
> map with the DEM included.  You mention that some sources of .hgt files
> contain voids.  Can you specify which ones you're aware of that should
> be avoided?
>
> Mark
>

Thanks Gerd!