Update dem.py to use NASADEM

[isce-framework]

Update dem.py to use NASADEM

Dear Prof. Fielding,

Actually, I have also the same problem in downloading the DEM file. When I checked this website (https://wiki.earthdata.nasa.gov/display/EL/How+To+Access+Data+With+cURL+And+Wget) and found that the configuration for the .netrc file should be the same as this website said.

Best regards,
Sayyed

[piyushrpt]

We are happy to take PRs with the required changes.

[EJFielding]

Before we start working on a Pull Request, we have to decide whether to simply change the dem.py code to use NASADEM or to add an option to use that while leaving the default as SRTM v3.
Any suggestions?

[piyushrpt]

The code should already work if a demstitcher.xml (or appropriately named xml) is created with the right base url in the folder where processing is being done. I assumed the suggestion was to change default to NASADEM.

[dbekaert]

@EJFielding believe changes would be:

1. Add NASA DEM as an option to dem.py - i.e. add it to the input parser
   Believe the -s and -t arguments here:

   isce2/applications/dem.py

   Line 66 in c92759a

   parser.add_argument('-s', '--source', type = int, default = 1, dest = 'source', help = 'Dem SRTM source. Possible values 1 or 3 (default: %(default)s)')

2. Similar as to the past here woudl be the location for the URL and the extensions of the tiles:
   https://github.com/isce-framework/isce2/blob/master/contrib/demUtils/demstitcher/DemStitcherV3.py

3. As the DEM is still behing earthdata log-on the rest shoudl work fine for pulling in tiles.
   

   isce2/contrib/demUtils/demstitcher/DemStitcherV3.py

   Line 156 in c92759a

   command = 'curl -n -L -c $HOME/.earthdatacookie -b $HOME/.earthdatacookie -k -f -O ' + os.path.join(url,fileNow)

   
   The extension is critical as otherwise it will not find the nasadem tiles. Would recommend you try and construct it and then manual try to see if its correct with the online tile.

4. Will let @piyushrpt to provide some guidance on keeping backward compatibility.

[piyushrpt]

I think this is similar to adding a sensor.

1. Add a new DEMStitcher in location that David pointed to. This stitcher handles the file naming weirdness - prefix, postfix, extra tags etc whatever it takes to build the right tile name.
2. Then this is exposed via the init.py in demUtils folder - createDemStitcher method.
3. Then type argument for dem.py (defaults to version3) can be set to nasadem and interface should work

[sssangha]

@EJFielding I have made the above suggested updates under the PR "sss_nasadem"

[piyushrpt]

Fixed in #118

[EJFielding]

Thanks!