[mkgmap-dev] How to handle missing hgt files or fileswith voids?

Mon Jan 15 11:37:25 GMT 2018

For Europe is a good source for 1 sec. hgt  EPSG 4326 : 
http://opendem.info/opendemeu_download_4326.html .
Thomas

--------------------------------------------------
Von: "Gerd Petermann" <gpetermann_muenchen at hotmail.com>
Datum: Montag, 15. Januar 2018 08:55
An: "Development list for mkgmap" <mkgmap-dev at 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-bounces at lists.mkgmap.org.uk> im Auftrag von 
> Henning Scholland <osm at 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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