[mkgmap-dev] WG: r4015 in dem-tdb branch implements --x-overview-dem-dist

Sat Dec 23 11:55:39 GMT 2017

Hi, although I use 3" hgt files, 3312 looks much more detailed than 9942?

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Van: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> namens Gerd Petermann <GPetermann_muenchen at hotmail.com>
Verzonden: zaterdag 23 december 2017 03:33:30
Aan: Development list for mkgmap
Onderwerp: [mkgmap-dev] WG: r4015 in dem-tdb branch implements --x-overview-dem-dist

Hi!
I've just noticed that I replied to Minko instead of the list. Please see below.

Gerd

________________________________________
Von: Gerd Petermann <gpetermann_muenchen at hotmail.com>
Gesendet: Samstag, 23. Dezember 2017 12:04
An: lig fietser
Betreff: AW: [mkgmap-dev] r4015 in dem-tdb branch implements    --x-overview-dem-dist

I am not sure what to think about that.
When you use 3'' hgt files (size is  ~2.8MB) the resolution in that data is 2^32/(360 * 1200) ~ 9942.
When you use 1'' hgt files (size is  ~26MB) the resolution in that data is 2^32/(360 * 3600) ~ 3314.
The current implementation in mkgmap interpolates the values found in the hgt file. It assumes
continous slope between two points at the same lat, so e.g. if one is 123 and the other is 135,
it assumes that a point in the middle is at 129.
I assumed that the Garmin algo does something similar when calculating the heights, but maybe it
doesn't.

I did not yet try to find out the best values for dem-dists, so it would be good to hear about results.

Gerd

________________________________________
Von: lig fietser <ligfietser at hotmail.com>
Gesendet: Samstag, 23. Dezember 2017 11:45:21
An: Gerd Petermann
Betreff: Re: [mkgmap-dev] r4015 in dem-tdb branch implements    --x-overview-dem-dist

Thanks Gerd, the value of 3312 works much better now!

________________________________
Van: Gerd Petermann <gpetermann_muenchen at hotmail.com>
Verzonden: zaterdag 23 december 2017 02:36:32
Aan: lig fietser
Onderwerp: AW: [mkgmap-dev] r4015 in dem-tdb branch implements --x-overview-dem-dist

Hi Minko,

to convert the parms for BuildDEMFile you have to multiply by 2^32/360 :
0.00027761 * 2^32/360  ~ 3312.

Gerd

________________________________________
Von: lig fietser <ligfietser at hotmail.com>
Gesendet: Samstag, 23. Dezember 2017 11:30:20
An: Gerd Petermann; Development list for mkgmap
Betreff: Re: [mkgmap-dev] r4015 in dem-tdb branch implements    --x-overview-dem-dist

Hi Gerd,
Thanks for the good work to implement DEM into mkgmap!
I have tested a few tiles, I noticed that BuildDEMFile with--dlon=0.00027761 has a much more detailed relief than the default values x-dem-dists=5520, 16560, 44176, 88368 How can I get the same results as with dlon=0.00027761?
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