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s-expression for EO product band math

Development

cd app-s-expression

Create the Python environment with mamba (faster) or conda (slower):

mamba env create -f environment.yml

Activate the Python environment with:

conda activate  env_app_snuggs

Build the Python project

To build and install the project locally:

python setup.py install

Test the CLI with:

s-expression --help

That returns:

$ s-expression --help
Usage: s-expression [OPTIONS]

  Applies s expressions to EO acquisitions

Options:
  -i, --input_reference PATH  Input product reference  [required]
  -s, --s-expression TEXT     s expression  [required]
  -b, --cbn TEXT              Common band name  [required]
  --help                      Show this message and exit.

Building the docker image

Build the docker image with:

docker build -t eoepca/s-expression:dev0.0.2  -f .docker/Dockerfile .

Test the CLI with:

docker run --rm -it eoepca/s-expression:dev0.0.2 s-expression --help

Usage

There are three application packages:

app-s-expression.cwl

This is the configuration exposing all the parameters:

  • input_reference This is the input product reference

  • s-expression This is the s-expression (see below what are s expressions)

  • cbn This is the common band name for the generated band

About the s-expressions:

In computer programming, S-expressions (or symbolic expressions, abbreviated as sexprs) are a notation for nested list (tree-structured) data, invented for and popularized by the programming language Lisp.

Here we use s-expression to express band combination operations on the EO product assets accessed using the common band names.

For instance, to do the normalized difference for the red and nir bands, this is expressed as:

(/ (- nir red) (+ nir red))

Let's break down the components of this s-expression:

  • (- nir red) is the difference between the nir and red assets read as array. This is equivalent to nir - red

  • (+ nir red) is the sum of nir and red assets read as array. This is equivalent to nir + red

  • The difference (- nir red) is divided by (+ nir red) to provide the NDVI with (/ (- nir red) (+ nir red))

So to do the NDVI, the app-s-expression.cwl CWL document can be invoked with:

input_reference: {class: Directory, path: '/workspace/stage-in/1_o28lv8'}
s_expression: '(/ (- nir red) (+ nir red))'
cbn: 'ndvi'

app-water-mask.cwl

The app-water-mask.cwl exposes a single parameter, input_reference and defines the arguments s-expression and cbn in the CWL document:

  • s-expression (where (>= (/ (- green nir) (+ green nir)) 0.3) 1 0)

  • cbn water-mask

app-ndvi.cwl

The app-ndvi.cwl exposes a single parameter, input_reference and defines the arguments s-expression and cbn in the CWL document:

  • s-expression (/ (- nir red) (+ nir red))

  • cbn ndvi