For Europe is a good source for 1 sec. hgt EPSG 4326 :
http://opendem.info/opendemeu_download_4326.html .
Thomas
--------------------------------------------------
Von: "Gerd Petermann" <gpetermann_muenc...@hotmail.com>
Datum: Montag, 15. Januar 2018 08:55
An: "Development list for mkgmap" <mkgmap-dev@lists.mkgmap.org.uk>
Betreff: Re: [mkgmap-dev] How to handle missing hgt files or fileswithvoids?>
Hi Henning,
checking data is not that easy, but I'll think about that option.
I'd like to add a short howto that describes ways to get good hgt data,
but I don't know any method for Windows users.
phyghtmap is good, but installation on Win is complex and doc for that
looks out-aged.
Srtm2Osm seems out-dated, as well as Groundtruth.
So, up to now I try to guess what areas I have to download from
viewfinder.
Any hints ?
Gerd
________________________________________
Von: mkgmap-dev <mkgmap-dev-boun...@lists.mkgmap.org.uk> im Auftrag von
Henning Scholland <o...@hscholland.de>
Gesendet: Montag, 15. Januar 2018 09:05:24
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] How to handle missing hgt files or files with
voids?
Hi Gerd,
regarding 1) I can create a list of existing tiles of Viewfinder (which
covers all land area so far I see). But it will be a long list. I remember
it's about 25000 files in total. So maybe it's easier to create a polygon
or at least take the list and let software create the polygon. An easier
way can be to check if data is available. No data might be sea. Of course
it's not 100% sure, as there are deserts and ferries.
Another idea I had during the weekend was to output a osm-file with
missing areas. So then user can check. But I came to conclusion, that it's
easily visible in the map later. So I'm not sure it's useful at all.
Henning
On 2018-01-15 15:45, Gerd Petermann wrote:
Hi all,
1) The current code (only) writes a log message with severity WARNING for
a missing hgt file:
"file xxx.hgt not found. Is expected to cover sea."
I wonder if we can create a list of files that can exist or maybe a
polygon that can be tested so that
tiles which are knwon to cover land are reported as errors.
When you look at
http://viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm
you can see that such a polygon would be quite complex.
Did anybody already try to define such a polygon or list of files that
would cover only ocean?
2) Should mkgmap print a warning when voids in the hgt file(s) have an
influence on the DEM data?
I think yes, but it is a bit more complex to measure the real effect.
Reason: We read the 4 hgt values next to the wanted DEM point and use
interpolation to calculate the height
that is stored in the DEM file.
If one or two of the 4 points are voids they may still have no influence
if the wanted point is very close to one that
is not a void. Another problem is that a single void might be used several
times.
So, another option would be to add an option like --dem-check-hgt which
could read all existing hgt files and
report the number of voids for each. I'd prefer this because it would have
no impact on performance for normal
processing. Or maybe there is already a tool for this that works on all
platforms (win,linux,mac) ?
Comments?
Gerd
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