SRTM files

[ppiter]

Hi,

I read about "offline altitude calculation from SRTM files is implemented as most wanted Idea on getSatisfaction ... (and bonus is direct automatic download of missing files from internet)" as a new feature. But I don't find a possibility to load the SRTM files in Locus. Can anyone give me a hint? Thank you
ppiter

[tommi]

It's available in Locus Pro >= 2.0.2.
Download can be triggered via "+ Fill altitude" for points or tracks from Locus' Data manager.

[Menion]

thanks tommi. If you'll want to download and use SRTM files manually, just put them into Locus/data/srtm directory

[brotbuexe]

Old: Where do we get the files? I understand the NASA have the files with a lower resolution for outside US.
New: Ok, I played with the function and found that its possible to download the needed files directly in Locus by just using the fill altitude (new features should be explained better in the whats new list .

----------

As I understand from https://de.wikipedia.org/wiki/SRTM-Daten the DLR have better resolution.
Also stated at: https://wiki.openstreetmap.org/wiki/SRTM
"It's more accurate than the data collected by NASA but covers only 40% of the planet. "

What format of the files do we need for locus?

It should be downloadable after registration from:
https://centaurus.caf.dlr.de:8443/eoweb ... tryPage.vm
The available data: https://centaurus.caf.dlr.de:8443/short ... index.html
You don't have to use real email, it doesnt need a activation process...
After registration and login the "download srtm data" button is active and you will get a page with a ftp link and some auto generated temporary login data (for 24 hours).

There is a pdf explaining the data, here is the content:

DLR SRTM Digital Elevation Models
General Information
This compressed archive contains individual digital elevation models (DEMs) covering a geographic
area of 10° by 10°. The filename of the archive specifies the bottom left coordinate of the 10° by 10°
tile. The elevation models were generated from X-band synthetic aperture radar (SAR) data acquired
during the Shuttle Radar Topography Mission (SRTM) in February of 2000. The corresponding SAR
image data are not included in the package. They can, however, be obtained via EOWEB-NG
(link:\eoweb.dlr.de:8080/index.html), the data portal of the German Remote Sensing Data Center at
the German Aerospace Center DLR.
In addition to the DEM files, the archive contains the corresponding height error maps (HEM), a
browse image map providing an overview of the area covered by the files contained in the archive, a
kml file for displaying the browse image of the coverage on Google Earth, and this 'Readme' file.
The Shuttle Radar Topography Mission - SRTM
The Shuttle Radar Topography Mission (SRTM) was conducted jointly between the German
Aerospace Center DLR, the Italian Space Agency ASI, and NASA JPL (USA). From February 11 to
22, 2000, two interferometric radar systems onboard the Space Shuttle Endeavor acquired data with
the goal of generating a global high resolution digital elevation model. The American system, operating
in C-band, was complemented by a higher resolution German-Italian X-band system.
The SRTM DEMs were generated using 'Radar interferometry' or 'InSAR'. Two X-band SAR antennas,
one inside the Space Shuttle cargo bay, the other at the end of a 60 m extension pole, simultaneously
acquired radar data. During the processing, the phase differences of the two corresponding datasets
were compared and converted into elevation values. An introduction to SAR interferometry can be
found at link:\mmm.gi.alaska.edu/~rgens/teaching/asf_seminar/intro_insar.pdf.
While the DEMs generated from the American C-band data are available through the USGS, the Xband
DEMs can be obtained via DLR.
Similar to the SRTM C-band data, the DLR/ASI X-band DEMs cover the entire globe between 60°
northern and southern latitude. However, the coverage of the X-band DEMs is not continuous. The
gaps between the individual criss-crossing image strips are a result of the higher precision and
therefore the narrow swath width of the X-band system. Information on the precise coverage of the
SRTM X-band data can be obtained by visiting the SRTM coverage page at
link:\mmm.dlr.de/srtm/level1/data_en.htm or by performing a data search for SRTM DEMs in EOWEBNG.
The SRTM project page provides additional information on the SRTM X-band mission
(link:\mmm.dlr.de/srtm/level1/start_en.htm). Further details on the mission in general, on technology,
accuracies, and applications are available in link:\www2.jpl.nasa.gov/srtm/SRTM_paper.pdf.
Since December of 2010 the X-Band SRTM DEMs are available at no cost. The data can be obtained
via EOWEB-NG (link:\eoweb.dlr.de:8080/index.html), the data portal of the German Remote Sensing
Data Center. A user can perform a traditional search in EOWEB-NG and order up to 100 datasets.
Additionally, the SRTM X-band DEMs can be downloaded in bulk from an FTP-Server, accessible via
a separate link after logging into EOWEB-NG.
DEM Information
The X-band SRTM DEM data are provided in DTED format. Detailed information on the DTED format
can be found in the document 'Product Description of the SRTM DTED-Format' (SRTM/PD-03/11/03)
available at link:\mmm.dlr.de/srtm/docs/SRTM-XSAR-DEM-DTED-1.1.pdf.
The DEM and HEM data are in geographic (Lat/Long) projection, datum WGS84. The elevation values
are also WGS84, as specified in the product description of the SRTM DTED-format.
The DEMs inside the compressed archive are distributed as individual files, i.e. they are not
mosaicked into one large DEM file. Each DEM covers an area of 15' by 15'. The filename of the
individual DEM file specifies the bottom left coordinate of the corresponding 15' by 15' DEM tile.
One pixel of the DEM files corresponds to approximately 25 m x 25 m on the ground. The elevation
values are provided at a resolution of 1 m. The horizontal accuracy of the SRTM X-band DEMs is ±20
m (abs.) / ±15 m (rel.), both 90% CE. The vertical accuracy is ±16 m (abs.) / ±6 m (rel.), both 90% LE.
Precise information on vertical and horizontal accuracies for individual tiles can be found in the
accuracy description record (ACC) of the DTED file.
As a result of the processing methodology a few locations within the DEM will have no data values.
These voids have not been removed in this particular product. Standard Remote Sensing image
processing tools, however, are able to compute and insert the missing values. The DEMs have not
been edited with respect to coastlines and water bodies. Therefore, coastlines may not be well defined
and water bodies may not be perfectly flat.
Legal Information
The use of the SRTM data is governed by the following usage conditions. By clicking on the button
'Download SRTM data' or by accessing the data via the FTP-link provided, you are accepting these
usage conditions.
The SRTM DEM data are intended primarily for scientific purposes. Redistribution of the original
SRTM data is not permitted, neither for commercial nor for non-commercial purposes. No further
restrictions, except for those contained herein, are being imposed on the usage of the data or derived
products.
The SRTM-X band DEMs have been processed to the highest possible standards of accuracy using
state-of-the-art technology. However, the data are provided as is. No warranty of any kind, whether
explicit or implied is given. Furthermore, as the SRTM data are provided free-of-charge, DLR shall not
be liable for any damage arising out of the SRTM data's usage. The user is responsible for observing
that no damage is caused to anyone or anything by his use of the SRTM data. By clicking on the
button 'Download SRTM data' or by accessing the data via the FTP-link provided, the user therefore
agrees to hold the German Aerospace Center (DLR) harmless from and against any and all claims
which might arise by himself or any third party out of the SRTM data's usage.
For all products based on the SRTM X-band data, and for all publications including these data or
derived products, it is mandatory to use the following copyright information: ©DLR/ASI <year of
production>.
----------------------------------
(I had to kill the links inside the text, because of too much urls in post message)

Its a little complicate for me to understand. The data I can download on ftp is still the old SRTM data thats also available at NASA, or is it the higher resolution for some areas?

If someone with more knowledge can explain...

Looks like I need the File E010N50.zip. The info pic shows a lot of holes, looks like they have no data for this areas? So its useless?
https://imgur.com/3vAyN

And I found another source with a "improved" version: http://srtm.csi.cgiar.org/

Still don't know which to use and what filetype.

[brotbuexe]

For documentation:

The NASA files:


US higher resolution: http://dds.cr.usgs.gov/srtm/version2_1/SRTM1/ see http://dds.cr.usgs.gov/srtm/version2_1/ ... nition.jpg

lower resolution:
http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/
see http://dds.cr.usgs.gov/srtm/version2_1/ ... nt_def.gif to get the degrees for the filenames for the areas you want.

[brotbuexe]

For simple downloading on the last server, use "DownThemAll" Extension in Firefox and a Regular Expression for the fileselection (put it in fast filtering:
For Germany: /(N48|N49|N50|N51|N52|N53|N54)(E006|E007|E008|E009|E010|E011|E012|E013|E014|E015)/ it selects 70 files, which gives 197 MB uncompressed hgt files.

[brotbuexe]

Short update.

https://en.wikipedia.org/wiki/Shuttle_R ... hy_Mission states that the NASA files had a holes with no data that where simply filled by interpolation. "The CGIAR-CSI version 4 provides the best global coverage full resolution SRTM dataset. "

I downloaded some (http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp used the the server from IT) , they have geotiff and arc info ascii. I don't know if its possible to support one of this filetypes directly in Locus.
There is at least one tool that convert to hgt (didn't test it): http://www.gdal.org/gdal_translate.html (Formats: http://www.gdal.org/formats_list.html). Because they are not the same size (1°x1° vs 5°x5°) there is some file-cutting needed.
If someone would try...

---------------------------

The Files from the DLR are in DT2 Format: http://www.gdal.org/frmt_dted.html
Filestructure:
E010N50HEME0194500N531500_SRTM_1_HEM.dt2 (Size 1,6MB)
and
E010N50DEME0194500N531500_SRTM_1_DEM.dt2 (Size 1,6MB)

A description: http://www.dlr.de/caf/Portaldata/60/Res ... ED-1.1.pdf
Because of the areas with no data and the small area they cover I decide to skip trying to use them.

[brotbuexe]

I searched a little and found a way to use the CGIAR Data v4.1 to create hgt files to use in locus.

It's a little complicated (windows only):

- First get the Arcinfo ASCII Grid Files (http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp)
  (The Kings College is actual not available but the links are like this http://srtm.geog.kcl.ac.uk/portal/srtm4 ... _38_03.zip and the server is fast, the available are slow...)
- Now unzip them in a folder
- Get "Microdem" (http://www.usna.edu/Users/oceano/pguth/ ... emdown.htm)
- Open the DEM Files via "File -> Open and Merge DEMs" (if you have more then one file)
- Select the .asc files (don't open too much at the same time (I opened 4))
- After a while it shows a window like:

[attachment=0:xlr46kh0]MAP.PNG[/attachment:xlr46kh0]

- Save a .bil file via "File -> Save DEM -> BIL"
- Get "BILxSRTM" (http://www.mediafire.com/?vuby9jvdk8r7drm)
- Use this tool to convert the BIL to a set of HDR Files.
- Use them in Locus...

Source of the howto (german): http://www.naviboard.de/vb/showthread.p ... 907&page=3

[brotbuexe]

For Information about the difference between SRTM data and CGIAR:
http://www.cgiar-csi.org/data/elevation ... tabase-v41

I needed about 30 minutes with install to create the about 70 hgt files (200 MB) for germany.

btw, if you want accurate data in the mountains, you can get hgt files for this area from: http://www.viewfinderpanoramas.org/dem3.html

[brotbuexe]

@menion, if possible, can you move my posts to the Tools section?

Back to the DLR Files with 1° resolution.
I downloaded them and can fill the holes they have with the data from cgiar.

East Germany:

[attachment=0:386qgw0f]greenshot_2012-04-25_17-46-09.png[/attachment:386qgw0f]


There is some line at the holes I don't know where they come from...

[attachment=1:386qgw0f]greenshot_2012-04-25_17-38-30.png[/attachment:386qgw0f]

The HGT files created with BILxSRTM are about 25 MB with 1° resolution instead of 3 MB for 3°.
Don't know for what this could be used.

Will try if it shows a better height graph on tracks when using them in locus. If locus can understand 1° resolution hgt files...
Anyone tried the SRTM 1° HGTs available for US?

[brotbuexe]

Comparison:

[attachment=0:3uq8me82]greenshot_2012-04-25_18-13-45.png[/attachment:3uq8me82]

Left the original SRTM data (Fill altitude online), right from the generated 1° hgt files.
Its all about 40-50 meter higher in the 1° version, don't know why...

When I check some peaks that have elevation, the data from SRTM is about 30m to low, the data from DLR is about 40m to high.