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

Thu Jan 25 12:03:41 GMT 2018

Hi Gerd

A binary file sounds very 'Garminesque' and if its a matter of speed 
then I would prefer such a format -

btw  has the --dem-interpolation option been implemented yet ?

Nick

On 25/01/2018 11:59, thesurveyor at wolke7.net wrote:
> Hi Gerd,
> first many thanks for your work on mkgmap.
> for the list of available hgt files: I prefer a human readable format
> Regards,
> Gert
> *Gesendet:* Donnerstag, 25. Januar 2018 um 12:40 Uhr
> *Von:* "Gerd Petermann" <gpetermann_muenchen at hotmail.com>
> *An:* "Development list for mkgmap" <mkgmap-dev at lists.mkgmap.org.uk>
> *Betreff:* Re: [mkgmap-dev] How to handle missing hgt files or files 
> with voids?
> Hi all,
>
> I've played with the list of available hgt files created by Henning.
> I've coded a reader for the list so that mkgmap can
> check if a missing hgt file should exist or if it covers ocean.
> The idea is to print a warning if a file was not found when it should be.
> The check is fast, but the list is long, so I wonder
> if I should store it "as is" in the mkgmap binary like we do with 
> LocatorConfig.xml
> or if I should use another format.
> The most obvious for me would be a binary file containing 180*360 
> bits, a 1 bit for every
> file that should exist.
>
> What do you think?
>
> Gerd
>
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag 
> von Gerd Petermann <gpetermann_muenchen at hotmail.com>
> Gesendet: Montag, 15. Januar 2018 14:25
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] How to handle missing hgt files or files 
> with voids?
>
> Hi Henning,
>
> I'll see if I can use srtm.zip.
> I think voids are interesting. When I started coding DEM support I 
> searched my PC for *.hgt files and found them in several places.
> Later I found out that some of those files have voids and that better 
> data exists (assuming that files without voids have fewer errors)
> So, I think it would be good to have a list of those files that have 
> voids.
>
> I'll see what is needed for this.
>
> 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 12:21:09
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: Re: [mkgmap-dev] How to handle missing hgt files or files 
> with voids?
>
> This would be the list of all hgt-files available on viewfinder.
>
> In each zip-file of viewfinder there are 6° in E-W direction and 3° in
> N-S. The scheme of naming is also simple. That list I also attached.
>
> In general I think it's better to just output a list, which
> hgt-files/viefinder-tiles are missing than writing a downloader. I mean
> in total it's 13GB of data. If you need to download it manually, you are
> more aware of what you are doing and not just download them all.
>
> Regarding voids: I think if there is a possibility the user can fix the
> hgt file, A list can be helpful. Otherwise I don't know if a list would
> be helpful. Only use case I see is to ask the user to use better data.
> But then we need a list, which source is best in which area. And finally
> all the different sources need to match each other. Otherwise it will
> lead to a hard border between 2 sources. I think this will be much to
> complicated...
>
> Maybe for advanced users there can be a Warning message, hgt-file
> N00E100.hgt contains 3 voids. So user can compare different sources
> manually.
>
> Henning
>
> On 15.01.2018 16:55, Gerd Petermann wrote:
> > 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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> >
> >
> >
> >
> > _______________________________________________
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> > mkgmap-dev at lists.mkgmap.org.uk
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> >
>
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