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[mkgmap-dev] HGT - getElevation()

From Gerd Petermann gpetermann_muenchen at hotmail.com on Mon Jan 15 07:05:24 GMT 2018

Hi Andrzej,

I think your patch increases the box too much. I think we only need an aligned upper left corner.
See my attached version.
Still, even with my patch DEM size can increase quite a lot. I've created a map of bolivia with without --dem-dists option.
Size of gmap folder:
223.511k with r4061
238.940k with r4061 + your patch
238.882k with r4061 + my patch

So, we have +15 MB for DEM with this alignment. I assume that the increase depends on the areas.list,
so maybe my one is a worse case.

Wouldn't it be better to change splitter so that it aligns tiles to HGT raster?


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej at poczta.onet.pl>
Gesendet: Sonntag, 14. Januar 2018 16:46:29
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] HGT - getElevation()

Hi Gerd,

 > you just want to achive that the calculated postions are as close as
 > possible to the positions in the hgt file

Yes. Linear interpolation is averaging too. If DEM can use exact values
form HGT, then there will be no averaging. Even interpolated values near
HGT node should be the same, because of rounding to 1m.

I have limited aligning to resolution better or equal 1200 and prepared
HGT area for worst case, which would be 1200. Patch attached.

Best regards,
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