<div dir="ltr"><div>Observation based on Austria:</div>Well if I create a map with DEM layer with resolution=0=24,1=23,2=22,3=21,4=20,5=19,6=18 and set dem-dists=6624 the resulting quality will be pretty low.<div>If I create that map instead with resolution=0=23,1=22,2:21.... and dem-dists=3312 - the filesize will be similar or actually smaller, the level of detail/quality of the DEM however much higher. Compared to the much bigger (in MB/filesize) option of
<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">0=24,1=23,2=22... and dem-dists=3312 there is virtually no visual difference in Basecamp.</span></div><div>Even with dem-dists=1656 there is no visual difference if you create the DEM layer starting with resolution 0=24 or 0=23. For dem-dists=3312 there is really no reason to go higher than resolution 23. Even resolution 22 would be fine. For dem-dists=1656 resolution 0=23 is good enough.</div><div><br></div><div>So actually if mkgmap could somehow make use of this to optimize the quality/size ratio of DEM layer that would be pretty good.</div><div>Even though dem-dists=1652 looks pretty neat in Basecamp - I'm not sure if it is not sometimes creating detail that is not there. For sure if you create a route and look at the altitude profile the overall climb/descent will be overstated - but that's of course also due to ways usually following more the possibility of lowest climb/descent vs shortest distance. In general the resolution of both OSM and DEM I guess is then not good enough and climb/descent will be overestimated a bit.</div><div><br></div><div>For Viewfinderpanormas 1" DEM files - the DEM produced with resolution 0=23 and dem-dists=3312 seems to be a good compromise if size is not a big factor. If size is a factor resolution 0=22 and dem-dists=3312 will be the optimum. For best visual quality resolution 0=23 and dem-dists=1656 will be best (though I'm not sure if we go for fake accuracy here. Resolution 0=24 and dem-dists=1562 is really not worth it. It maybe however that the 1"DEM is not up to actually improving quality for dem-dists=1656 in the Alps so best quality default would actually be resolution 0=23 dem-dists=3312 and best quality/size 0=22 and dem-dists=3312.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On 31 March 2018 at 13:00, Gerd Petermann <span dir="ltr"><<a href="mailto:gpetermann_muenchen@hotmail.com" target="_blank">gpetermann_muenchen@hotmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Felix,<br>
<br>
Sorry, I don't understand how you connect resolution and DEM. Can you explain this more detailed?<br>
<span class=""><br>
Gerd<br>
<br>
______________________________<wbr>__________<br>
Von: mkgmap-dev <<a href="mailto:mkgmap-dev-bounces@lists.mkgmap.org.uk">mkgmap-dev-bounces@lists.<wbr>mkgmap.org.uk</a>> im Auftrag von Felix Hartmann <<a href="mailto:extremecarver@gmail.com">extremecarver@gmail.com</a>><br>
</span>Gesendet: Samstag, 31. März 2018 12:33:44<br>
<span class="">An: Development list for mkgmap<br>
</span>Betreff: Re: [mkgmap-dev] DEM Resolution and size savings<br>
<span class=""><br>
Yes I know there are still improvements to be done. It was just a suggestion because the result is much better than saving space/data by decreasing the dem-dist value. Even resolution 22 as highest value is still pretty good - but with 22 on 3312 you start to see some very small changes already. Still way better than 6624 at resolution 24.<br>
Actually with resolution 22 it just looks a little bit flatter but level of detail still seems to be the same (similar to decreasing the elevation exageration by 20% in Basecamp). Only at resolution 21 you really start to miss detail (in general it seems to me that the DEM detail is not that good in Basecamp - but that also applies to original garmin maps).<br>
<br>
Maybe to save size (because right now DEM at resolution 24 can get quite huge) - there could be an option to have the DEM always saved like this - so same as 3312 on resolution 22 but at 24....<br>
<br>
</span><span class="">On 31 March 2018 at 08:40, Gerd Petermann <<a href="mailto:gpetermann_muenchen@hotmail.com">gpetermann_muenchen@hotmail.<wbr>com</a><mailto:<a href="mailto:gpetermann_muenchen@hotmail.com">gpetermann_<wbr>muenchen@hotmail.com</a>>> wrote:<br>
Hi Felix,<br>
<br>
yes, the DEM format is not yet fully understood. I assume what you have is a map that uses a shrink factor <> 1.<br>
The shrink factor is used like this:<br>
The height deltas are devided by this value before encoding and multiplied when extracting. The effect is that the deltas<br>
are smaller and therefore the size is also smaller, but of course you also lose a bit of information, because only the integer<br>
part is stored.<br>
The problem is that Garmin also uses slightly different rules for the encoder, and we did not yet find out all details.<br>
Frank Stinners program BuildDEMFile allows to use this but sometimes produces invalid data.<br>
The tool DemDisplay shows my current knowledge.<br>
<br>
Gerd<br>
<br>
______________________________<wbr>__________<br>
</span>Von: mkgmap-dev <<a href="mailto:mkgmap-dev-bounces@lists.mkgmap.org.uk">mkgmap-dev-bounces@lists.<wbr>mkgmap.org.uk</a><mailto:<a href="mailto:mkgmap-dev-bounces@lists.mkgmap.org.uk">mkgmap-<wbr>dev-bounces@lists.mkgmap.org.<wbr>uk</a>>> im Auftrag von Felix Hartmann <<a href="mailto:extremecarver@gmail.com">extremecarver@gmail.com</a><<wbr>mailto:<a href="mailto:extremecarver@gmail.com">extremecarver@gmail.com</a><wbr>>><br>
<span class="">Gesendet: Freitag, 30. März 2018 23:07:10<br>
An: Development list for mkgmap<br>
Betreff: [mkgmap-dev] DEM Resolution and size savings<br>
<br>
Hi everyone,<br>
<br>
I noticed that the DEM layer if created for resolution 23 only (with a map that has not 24 resolution) will only be half the size of the DEM in resolution 24 (dem-dist=3312) - however in Basecamp/Mapsource the detail is virtually identical - I cannot see any difference in quality.<br>
<br>
<br>
So I think there must be some way to still save a lot of data/space - but it's not by going for dem-dits=6624 - that will result in much worse DEM detail.<br>
<br>
(I still really haven't found a good solution for DEM on GPS devices though. Need more time trying out different values and possibilities. Right now I think best is probably a separate transparent but except for DEM empty DEM only gmapsupp.img).<br>
<br>
--<br>
Felix Hartman - Openmtbmap.org & VeloMap.org<br>
Schusterbergweg 32/8<br>
6020 Innsbruck<br>
Austria - Österreich<br>
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<br>
<br>
<br>
--<br>
Felix Hartman - Openmtbmap.org & VeloMap.org<br>
Schusterbergweg 32/8<br>
6020 Innsbruck<br>
Austria - Österreich<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div><div>Felix Hartman - Openmtbmap.org & VeloMap.org<br></div>Schusterbergweg 32/8<br></div><div>6020 Innsbruck<br></div></div>Austria - Österreich</div></div></div></div>
</div>