Author Topic: [Q] How to get the right information about altitude  (Read 7806 times)

Offline Christian

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[Q] How to get the right information about altitude
« on: February 07, 2015, 18:26:00 »
Hi guys,
first of all, i know the altitude manager in Locus, STRM files, barometric and gps stuff a.s.o. to get altitude values out of Locus.
In the heart of middle Frankonia sometimes i used to do trailrunning and want to know the exact altitude differences to plan my routes.
As you can see on osm there is a small canyon called Schwarzachklamm with a bridge 18m in height and the canyon is accordingly 18m deep. Very nice there.
The height lines on osm maps and on vector maps from Locus store based on osm doesn't show any hillsides inside the canyon. Means, all the lines parallel to the the creek are missed. Due to the heigth below 20m there are no information about altitude differences.

Example: if i use "add / meaure route" and across the creek or moving the center cross over the creek and over the hillside i get 5m height difference only.
If i choose the path by feet up and downstairs i get 16m downhill and 16m uphill as real numbers (not in Locus). Doing this recurrently i get a lot of height meters but not noticed by Locus.

This problem seems bigger to me than don't know the exact altitude of the Schwarzachklamm yet. In landscapes with rippled surfaces and altitude differences <20m like in average mountain or foreland of the alps  there are no exact values on maps and in SRTM files also.


How to get the information about the exact altitude?
Any hints?

Christian

 

Offline voldapet

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Re: [Q] How to get the right information about altitude
« Reply #1 on: February 10, 2015, 09:58:05 »
Hello Christian,

It seems that you know the SRTM data. Locus and probably OpenCycleMap use similar data for contour lines. Locus use SRTM3 dataset which you can imagine as grid of points on Earth surface. This grid has resolution approximately 90 meters. Narrow canyon may not influence the altitude or contour lines because simple there are no data from the canyon. I have to also notice that accuracy of SRTM data in elevation is about 5 - 10 meters. This is another reason why canyon may not be "visible" in the data.
SRTM can not detect such small changes in earth surface.
 

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #2 on: February 10, 2015, 17:49:09 »
Thank you Petr for explanation.SRTM3 is th crux.
USGS has released SRTM1 for public in 09/2014. Is this supported by Locus? If so i will try to download via earthexplorer...
 

Offline voldapet

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Re: [Q] How to get the right information about altitude
« Reply #3 on: February 11, 2015, 09:24:39 »
Yes, Locus is able to read the SRTM1 hgt files. Put them into folder Locus/data/SRTM as standartd SRTM3 files. And thank you for information about release SRTM1 for rest of the world - I didn't know it. Honestly not sure if we use it because SRTM1 files have 10x bigger size then SRTM3 files. We also had  some troubles with contour lines on the border of coverage of SRTM3 and SRTM1 areas. Hovewer good to know. Thank you.
 

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #4 on: February 11, 2015, 19:13:14 »
Downloading SRTM files from USGS is a mess :(
ok, there are no .hgt files. Only .bil, .blw, .hdr, .prj in BIL-files.
Additional there are .dt2 as DTED and GEOTIFF.
Wich files are needed?
 

Offline voldapet

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Re: [Q] How to get the right information about altitude
« Reply #5 on: February 12, 2015, 09:38:30 »
You need the *.hgt files but honestly we didn't download them from NASA or USGS. Please see http://www.viewfinderpanoramas.org/dem3.html  where is possible to download *.hgt file in packages for bigger areas. But it seems that new released SRTM1 files aren't available here. So sorry I can't give you any clue where or how to download new SRTM1 data. But if you find out how to download them ..I'd like to know it :)
 

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #6 on: February 12, 2015, 09:52:56 »
:(
Thanx.
 

Offline popej

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Re: [Q] How to get the right information about altitude
« Reply #7 on: February 12, 2015, 16:48:14 »
Site for downloading SRTM v3 is here:
https://lpdaac.usgs.gov/data_access/data_pool/

Direct links to SRTM1 look like this:
http://e4ftl01.cr.usgs.gov/SRTM/SRTMGL1.003/2000.02.11/N49E020.SRTMGL1.hgt.zip

And to SRTM3:
http://e4ftl01.cr.usgs.gov/SRTM/SRTMGL3.003/2000.02.11//N49E020.SRTMGL3.hgt.zip


FYI server shows following warning at directory listing:

                         U.S. GOVERNMENT COMPUTER

This US Government computer is for authorized users only.  By accessing this
system you are consenting to complete monitoring with no expectation of privacy.
Unauthorized access or use may subject you to disciplinary action and criminal
prosecution.
popej
 

Offline gynta

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Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #9 on: February 12, 2015, 22:17:19 »
just creating SRTM1 .hgt files :)
New files quite huge. How to change the path to store the SRTM data on external SD? I didn't find anything in config file.
Will write a small tutorial after testing...
 

Offline gynta

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Re: [Q] How to get the right information about altitude
« Reply #10 on: February 12, 2015, 22:57:50 »
Try
Settings->Misc->default dirs

btw.
All testings already done before.
...years ago :)
« Last Edit: February 12, 2015, 23:01:14 by gynta »
 

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #11 on: February 12, 2015, 23:16:27 »
Thanx. Never thought that settings available in UI. Great job menion!
What did you test? public SRTM1 data?

ok, SRTM1 works in Locus.
 

Offline gynta

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Re: [Q] How to get the right information about altitude
« Reply #12 on: February 12, 2015, 23:20:08 »
What did you test? public SRTM1 data?
Sure, that stuff is not new :)

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #13 on: February 12, 2015, 23:27:44 »
small tutorial
how to get SRTM1 data as .hgt files working in Locus

: go to  www.http://earthexplorer.usgs.gov/ (download from DLR not working 'cause download link is broken)
: enable cookies in your browser
: register as user, tell them all the things they want to know (color of underwear, last sex...)
: choose Digital elevation model -> SRTM1
: choose area where you want to download elevation files by polygon tool from map or use shape file if available
: follow process, stay calm
: bulk download doesn't work for me (and you have to install a bulk downloader at first and download doesn't work either)
: download each file in BIL-format manually: *_bil.zip (5MB each)
: unzip all *_bil.zip in one folder (one zip contains 5 files)

: go to http://www.mediafire.com/download/vuby9jvdk8r7drm/BILxSRTM.zip
: download zip file and unzip
: start BILxSRTM.exe
: choose folder with unzipped .bil files
: choose folder where hgt files should be stored
: press start and create hgt files. New hgt files have 25,7MB each. If you fear to run out of storage in your phone:
: create new folder on externalSDcard
: copy hgt files to external SD card of your phone
: set new path to SRTM files in Locus settings-> misc-> Locus/srtm
: restart Locus
enjoy new elevation values.

First test:
works smoothly. Got more meters uphill and downhill in statistics of an existing track.
« Last Edit: February 12, 2015, 23:30:42 by Christian »
 

Offline Christian

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Re: [Q] How to get the right information about altitude
« Reply #14 on: February 12, 2015, 23:30:10 »
What did you test? public SRTM1 data?
Sure, that stuff is not new :)

SRTM1 data were released September 2014 for public.
???