[mkgmap-dev] DEM Default Levels

Thu Mar 22 05:57:43 GMT 2018

I also think that hillshading on the device is only useful when you zoom out a lot, don't remember the actual values.
I have a basemap on my oregon which seems good enough for that.
I think there is no direct connection between DEM data and the (RGN) levels, but Frank Stinners pdf [1] claims that this is the case.
See page 27 for more details.
I might know more in a few months after my next long cycle tour. Basecamp is happy with only one DEM level  but uses
more if available, for example the DEM level used to calculate the elevation profile depends on the length of the route,
the longer the more likely Basecamp selects DEM with lower resolution. Never tried that on the device. I also did not try
any 3D functions so far.

In [2] I described how you can create DEM only tiles and use them to reduce computation time. I think this should still work.

Gerd

[1] https://github.com/FSofTlpz/Garmin-DEM-Build/blob/master/DEM-Daten.pdf
[2] http://gis.19327.n8.nabble.com/Performance-with-zipped-hgt-files-tp5909756p5909801.html

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Felix Hartmann <extremecarver at gmail.com>
Gesendet: Mittwoch, 21. März 2018 23:01:43
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] DEM Default Levels

oh yeah - how could I actually exclude DEM at level 24? (with intention to still show in Basecamp/Mapsource, but not on device for level 24). So a map with DEM only 23-19, while overall resolution of map is 24-18....

On 21 March 2018 at 23:00, Felix Hartmann <extremecarver at gmail.com<mailto:extremecarver at gmail.com>> wrote:
Well I actually think hillshading is most useful when looking at zoom levels 20km to 200m or 120m - any closer and it just makes the map darker without actually improving to recognize contours at all. Right now with no input given I ended up with 20km to 200/300m no shading, then shading until the closest zoomed in. Exactly the opposite of what I would feel is ideal.
Okay so I will try around a bit too.

BTW - I tried to create empty map with DEM only. Basecamp and Mapsource don't like it (gave the typical error - there is not enough space on device, sending XX MB free XXXX). It does work without problems in Basecamp/Mapsource though for display. Would be quite practical to just hand mkgmap readymade empty DEM .img files for saving time on map compilation.

On 21 March 2018 at 22:53, Gerd Petermann <gpetermann_muenchen at hotmail.com<mailto:gpetermann_muenchen at hotmail.com>> wrote:
Hi Felix,

I still have no idea how to calculate reasonable values. So far nobody proposed a formular, and Garmin also uses
different values in different maps. So, I think the sample given in the help is a good start. I did not see a problem in
my Oregon with a map having 4 levels and DEM with only 2 levels, I think it all depends on personal preferences.
Anyway, I'd be happy to implement a default if the community agrees on something, so feel free to sugeest a formular.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk<mailto:mkgmap-dev-bounces at lists.mkgmap.org.uk>> im Auftrag von Felix Hartmann <extremecarver at gmail.com<mailto:extremecarver at gmail.com>>
Gesendet: Mittwoch, 21. März 2018 22:32:56
An: Development list for mkgmap
Betreff: [mkgmap-dev] DEM Default Levels

I'm a bit unclear about the --dem-dists command.
It says that at default it chooses sensible values based on .hgt file. Could there be an option to by default choose sensible levels based on .hgt AND --levels command?

As far as I can see depending on hgt default will go to show from very zoomed in to 200 or 300m on Oregon 600 (map detail=normal/default).

Now should I just calculate the values for my levels based on the help file no matter the input files? Some maps of mine, e.g. Alps use Viewfinder 1" and 3" or SRTM 1" and 3" so if this is related to the .hgt file resolution it is not very clear what happens with mixed input files.

Could the default be changed to calculate proper values for --levels or add a value like --dem-dists=levels that chooses sensible defaults? I guess that would be the easiest solution.

--
Felix Hartman - Openmtbmap.org & VeloMap.org
Schusterbergweg 32/8
6020 Innsbruck
Austria - Österreich
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--
Felix Hartman - Openmtbmap.org & VeloMap.org
Schusterbergweg 32/8
6020 Innsbruck
Austria - Österreich

--
Felix Hartman - Openmtbmap.org & VeloMap.org
Schusterbergweg 32/8
6020 Innsbruck
Austria - Österreich