Create upsampled DEMs for InSAR processing
Project description
DEM creator
Tool for making Digital Elevation Maps (DEMs) in binary data format (16-bit integers, little endian) for use in Interferometric SAR (InSAR) processing
sardem
creates a cropped (and possibly upsampled) digital elevation map:
usage: sardem [-h] [--bbox left bottom right top] [--geojson GEOJSON] [--xrate XRATE] [--yrate YRATE] [--output OUTPUT] [--data-source {NASA,NASA_WATER,AWS}]
[--convert-to-wgs84]
[left_lon] [top_lat] [dlon] [dlat]
Setup and installation
pip install sardem
This creates the command line executable sardem
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
$ sardem --help
usage: sardem [-h] [--bbox left bottom right top] [--geojson GEOJSON] [--xrate XRATE] [--yrate YRATE] [--output OUTPUT] [--data-source {NASA,NASA_WATER,AWS}]
[--convert-to-wgs84]
[left_lon] [top_lat] [dlon] [dlat]
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:
sardem --bbox -156 18.8 -154.7 20.3 # bounding box: left bottom right top
sardem -156.0 20.2 1 2 --xrate 2 --yrate 2 # Makes a box 1 degree wide, 2 deg high
sardem --geojson dem_area.geojson -x 11 -y 3
sardem -156.0 20.2 0.5 0.5 -r 10 --data-source NASA_WATER -o my_watermask.wbd # Water mask
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
--bbox left bottom right top
Bounding box of area of interest (e.g. --bbox -106.1 30.1 -103.1 33.1 ).
--geojson GEOJSON, -g GEOJSON
Alternate to corner/dlon/dlat box specification:
File containing the geojson object for DEM bounds
--xrate XRATE, -x XRATE
Rate in x dir to upsample DEM (default=1, no upsampling)
--yrate YRATE, -y YRATE
Rate in y dir to upsample DEM (default=1, no upsampling)
--output OUTPUT, -o OUTPUT
Name of output dem file (default=elevation.dem for DEM, watermask.wbd for water mask)
--data-source {NASA,NASA_WATER,AWS}, -d {NASA,NASA_WATER,AWS}
Source of SRTM data (default NASA). See README for more.
--convert-to-wgs84, -c
Convert the DEM heights from geoid heights above EGM96 to heights above WGS84 ellipsoid
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
and sardem/download.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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