16.4. bathy_threshold_calc.py

The bathy_threshold_calc.py program takes as input a single-channel image, for example, band 7 of a WorldView multispectral image, and computes the threshold separating the water and land pixels.

See Section 8.26.3 for further context, and a sample output and graph.

This tool needs Python 3 and some additional Python packages to be installed with conda.

Conda can be obtained from

https://docs.conda.io/en/latest/miniconda.html

Run:

./Miniconda3-latest-Linux-x86_64.sh

on Linux, and the appropriate version on OSX (this script needs to be made executable first). Use the suggested:

$HOME/miniconda3

directory for installation.

Next, with the conda environment activated, the needed packages can be installed as follows:

conda create --name bathy -c conda-forge python=3.6 gdal
conda activate bathy
conda install -c conda-forge numpy scipy matplotlib

This program can be invoked as:

~/miniconda3/envs/bathy/bin/python $(which bathy_threshold_calc.py) \
    --image image.tif --num-samples 1000000

Here it is assumed that ASP’s bin directory is in the path, otherwise the full path to this Python script must be specified above.

Command-line options for bathy_threshold_calc.py:

-h, --help

Display the help message.

--image <filename>

The single-channel image to use to find the water-land threshold.

--num-samples <integer (default: 1000000)>

The number of samples to pick from the image (more samples will result in more accuracy but will be slower).

--no-plot

Do not show the plot.