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Altitude (and 3D) with ASTER GDEM (Tutorial)

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Post  yip on Tue Oct 30, 2012 1:36 pm

Hello

The app orux recommends (High Altitude) keeps crashing on my device, so here is another way.

Moreover, AFAIK, the app provides only SRTM data, and contain ads, therefore less trustable .
AFAIK, SRTM is limited to 90m resolution outside the USA.

the ASTER GDEM dataset has 30m resolution worldwide, wich is better.
ASTER DEM is distributed by the NASA and a Japanese organisation.

the dataset consists of GeoTiff format, so those would need to be converted to HGT.
Pre- requisites:
You will need the GDAL tools ( http://www.gdal.org/ ) to convert them. I suggest using linux as this is the easiest way to get them.

1/ Create an account there : https://reverb.echo.nasa.gov/reverb/users/new
2/ go there : http://gdex.cr.usgs.gov/gdex/ and sign in with the account you just created.
3/ select the area you want using the interface. there is a limit, so don't select over 300kmx300km or so.
4/ click the button "Download data", it is the last of the small ones at the top.
5/ A box pop up. Select "ASTER GDEM v2" and "Geotiff 1x1 tile", check .zip, choose a research area, and hit Submit
6/ Another box pop up after a few seconds, hit Download

Ok, you now have the files ! Now, we need to convert them to HGT, so Oruxmaps can read them.

7/ Download and install GDAL (on linux, it can be as simple as "apt-get install gdal-bin")
8/ for each ASTGTM2_N000E000_dem.tif file, execute this command:
gdal_translate -of SRTMHGT ASTGTM2_N000E000_dem.tif N000E000.HGT
(The numbers in red will be different for each files)

Copy all the HGT files in the oruxmaps/dem folder an it's done !

Yeah, it is a little tedious to execute the command for EVERY file, next step is writing a nice little shell/dos script that will handle that.

Info: each tile is about 25Mb and covers about 40km²

Thanks the NASA for making this data available !
On the old continent, this sort of data, even when 100% public-founded, is unavailable or sold for profit at best Evil or Very Mad so you pay twice the data, first with taxes, then with cash.
The french IGN has made available a DEM at a resolution of 250m (BD alti) in an act of goodwill. pathetic.

yip

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Altitude (and 3D) with ASTER GDEM (Tutorial) Empty Re: Altitude (and 3D) with ASTER GDEM (Tutorial)

Post  drmrbrewer on Mon Dec 24, 2012 8:33 pm

Thanks for this tutorial. Very helpful.

Mike

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