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 8.27.3 for further context, and a sample output and graph.

16.4.1. Example usage

Install the bathy conda environment as described in Section 16.4.2 below.

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.

16.4.2. Dependencies

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.

Activate conda. 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

16.4.3. 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.