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[mkgmap-dev] HGT - getElevation()

From Gerd Petermann gpetermann_muenchen at hotmail.com on Tue Jan 16 20:32:09 GMT 2018

Hi Andrzej,

can you explain in detail what you did? Did you use patched mkgmap for this?

reg. testing: My current thinking is that we should look at the height values displayed
at the status line when in highest zoom (20m). For example, create a map that contains
an area around -20.0 -64.0 , use Strg+T to jump to exactly
S20 W64 , make sure that the cursor is in the crosshair and it should display 1284m because
that is the value that I find as 1st value in s21w064.hgt (it starts with 0x0504).
Repeat this procedure with different maps, one with bbox aligned, one with a large difference
(1/2 hgt pixel width, maybe also 1/3 and 3/4 or so).
All this with unpatched and patched r4068.
I assume that we get the best result with an input file that has a bounds statement
which places the upper left corner as close as possible to the hgt raster.

Does that make sense?


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej at poczta.onet.pl>
Gesendet: Dienstag, 16. Januar 2018 16:36:22
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] HGT - getElevation()

Hi Gerd,

I have tried to align pbf bbox with HGT. I have ceated 2 maps, one with
god alignment and second with left and top edge moved by 1/2 HGT pixel
size. I have used HGT with resolution 3600, so the movement was about
15m. I think shading is the same on both maps. There is no obvious
change, but I can't make BaseCamp to display maps at exactly the same
position, so there is a small movement of all objects. See pictures:

DEM layer is the same for both maps, position and size exactly the same.

I have found, why shading on your map looks more detailed. You have
created only single layer of DEM, while I use 4 layers. Shading with
multiple layers looks softer. Another weird effect is that with single
layer, shading gets softer, when you set "Map Detail" to higher in
Mapsource. With multilayer is opposite, probably Mapsource switches
between layers.

Best regards,
mkgmap-dev mailing list
mkgmap-dev at lists.mkgmap.org.uk

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