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Create upsampled DEMs for InSAR processing

Project description

Build Status Coverage Status

DEM creator

Tool for making Digital Elevation Maps (DEMs) in Roipac data format (16-bit integers, little endian) for use in Interferometric SAR (InSAR) processing

createdem creates a cropped (and possibly upsampled) digital elevation map:

usage: createdem left_lon top_lat dlon dlat
                 [-h] [--rate RATE=1] [--output OUTPUT=elevation.dem]
                 [--data-source {NASA,AWS}]

Setup and installation

pip install sardem

This creates the command line executable createdem

Alternatively, you can clone to build/install:

git clone https://github.com/scottstanie/sardem
cd sardem
make

which will run pip install --upgrade . and create the command line script.

If you use virtualenv

# Optional for using virtualenv
virtualenv ~/envs/sardem && source ~/envs/sardem/bin/activate  # Or wherever you store your virtual envs
# Or if you have virtualenv wrapper: mkvirtualenv sardem
pip install sardem

Command Line Interface

The full options for the command line tool in sardem/cli.py can be found using

$ createdem --help
usage: createdem left_lon top_lat dlon dlat
                 [-h] [--rate RATE=1] [--output OUTPUT=elevation.dem]
                 [--data-source {NASA,AWS}]


Stiches SRTM .hgt files to make (upsampled) DEM

    Pick a lat/lon bounding box for a DEM, and it will download
    the necessary SRTM1 tiles, stitch together, then upsample.

    Usage Examples:
        createdem -156.0 20.2 1 2 --rate 2  # Makes a box 1 degree wide, 2 deg high
        createdem -156.0 20.2 0.5 0.5 -r 10 --data-source NASA -o my_elevation.dem

    Default out is elevation.dem for the final upsampled DEM.
    Also creates elevation.dem.rsc with start lat/lon, stride, and other info.

positional arguments:
  left_lon              Left (western) most longitude of DEM box (degrees, west=negative)
  top_lat               Top (northern) most latitude of DEM box (degrees)
  dlon                  Width of DEM box (degrees)
  dlat                  Height of DEM box (degrees)

optional arguments:
  -h, --help            show this help message and exit
  --rate RATE, -r RATE  Rate at which to upsample DEM (default=1, no upsampling)
  --output OUTPUT, -o OUTPUT
                        Name of output dem file (default=elevation.dem)
  --data-source {NASA,AWS}, -d {NASA,AWS}
                        Source of SRTM data (default NASA). See README for more.

The code used for bilinear interpolation in the upsampling routine is in cython/upsample.c, and is wrapped in cython to allow easier installation and ability to call the function from Python. The installation is handled through pip install, or by running make build.

Functions for working with digital elevation maps (DEMs) are mostly contained in the Downloader and Stitcher classes within sardem/dem.py.

NASA SRTM Data access

The default datasource is NASA's SRTM version 3 global 1 degree data. See https://lpdaac.usgs.gov/dataset_discovery/measures/measures_products_table/srtmgl3s_v003 . The data is valid outside of artic regions (-60 to 60 degrees latitude), and is zeros over open ocean.

This data requires a username and password from here: https://urs.earthdata.nasa.gov/users/new

You will be prompted for a username and password when running with NASA data. It will save into your ~/.netrc file for future use, which means you will not have to enter a username and password any subsequent times. The entry will look like this:

machine urs.earthdata.nasa.gov
    login USERNAME
    password PASSWORD

If you want to avoid this entirely, you can use Mapzen's data hosted on AWS by specifying

sardem 156.0 20.0 .5 0.5 --data-source AWS

--data-source NASA is the default.

Mapzen combines SRTM data with other sources, so the .hgt files will be slightly different (but often not noticeable)

Warning: Mapzen notes that they are discontinuing some services, which is why NASA is the default.

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