Data Services Swath Projector

To download source code:

git clone https://github.com/nasa/harmony-swath-projector

To build the Docker image:

cd harmony-swath-projector
./bin/build-image

Directory contents:

• .snyk - A file used by the Snyk webhook to ensure the correct version of Python is used when installing the full dependency tree for the Swath Projector. This file should be updated when the version of Python is updated in the service Docker image.
• bin - A directory containing scripts to build and run Docker images. This includes the service and test Docker images.
• docs - A directory containing documentations, primarily in Jupyter notebooks.
• docker - A directory containing the service and test Dockerfiles.
• pip_requirements.txt - A file containing third party packages to be installed via Pip.
• swath_projector - A directory containing the source code for the service.
• tests - A directory containing a Python unit-test suite.

Running the Swath Projector:

The Swath Projector can be run and tested as part of a local installation of Harmony. See https://github.com/nasa/harmony/blob/main/README.md for more details.

To run the service locally, by invoking the Python module directly.

First ensure you are in a conda environment, with the conda and Pip dependencies installed, as specified in their requirements files.

conda create --name=swathprojector python=3.11 -q \
    --channel conda-forge --channel defaults -y
conda activate swathprojector
pip install -r pip_requirements.txt

For simple invocations, you can then use the bin.project_local_granule Python module:

$ cd harmony-swath-projector
$ python
>>> from bin.project_local_granule import project_granule
>>> project_granule('<full path to local granule, including: file:///>')

The project_granule function allows a user to specify the target Coordinate Reference System (CRS) and interpolation method. For more complicated requests a user can mimic the behavior of the project_granule script, but defining a custom input Harmony message with more parameters defined. When manually constructing and invoking a Harmony message, the environment variables ENV, OAUTH_CLIENT_ID, OAUTH_PASSWORD, OAUTH_REDIRECT_URI, STAGING_BUCKET and STAGING_PATH will need to be manually set. If ENV=dev or ENV=test, then the other environment variables can be set to anything. Be careful not to update these variables in the same environment as a locally running instance of Harmony.

Message schema:

The Swath Projector can specify several options for reprojection in the format property of the Harmony message:

{
  ...,
  "format": {
    "crs": "CRS:84",
    "interpolation": "bilinear",
    "width": 1000,
    "height": 500,
    "scaleExtent": {
      "x": {"min": -180, "max": 180},
	  "y": {"min": -90, "max": 90}
    },
    "scaleSize": {"x": 1, "y": 1}
  },
  ...
}

• crs: Either an EPSG code, or a Proj4 string. Default to geographic coordinates.
• interpolation: near, bilinear, ewa or ewa-nn. Currently defaults to ewa-nn, which uses elliptically weighted averaging to pick the value of the highest weighted pixel in relation to the output grid pixel.
• width: The number of output grid pixels in the x dimension. Should be used with height. The default value is the x scaleExtent divided by the x resolution.
• height: The number of output grid pixels in the y dimension. Should be used with width. The default value is the y scaleExtent divided by the y resolution.
• scaleExtent: An object for each of the x and y dimension of the image, specifying the minimum and maximum extent of that dimension in the reprojected CRS. If the scaleExtent is not specified, it is derived from the walking the perimeter of the input grid, reprojected those points to the target CRS, and finding the extreme values in each reprojected dimension.
• scaleSize: The resolution of each output pixel in the reprojected CRS. The default values are derived from finding the total area of the swath via Gauss' Area formula, and assuming the pixels are square. This should not normally be specified if the height and width are also supplied, in this case the grid definition must be internally consistent with itself. Where consistency is determined by the equation scaleSize = (scaleExtent.max - scaleExtent.min) / dimension

All the attributes in the format property are optional, and have defaults as described.

Development notes:

The Swath Projector runs within a Docker container (both the project itself, and the tests that are run for CI/CD). If you add a new Python package to be used within the Swath Projector (or remove a third party package), the change in dependencies will need to be recorded in the relevant requirements file:

• harmony-swath-projector/pip_requirements.txt: Additional requirements installed within the container's conda environment via Pip. These are also required for the source code of the Swath Projector to run.
• harmony-swath-projector/tests/pip_test_requirements.txt: Requirements only used while running tests, such as pylint or coverage. These are kept separate to reduce the dependencies in the delivered software.

Running tests:

The Swath Projector has Python tests that use the unittest package. These can be run within a Docker container using the following two scripts:

# Build a Docker image with all test files and dependencies
./bin/build-test

# Execute the `unittest` suite within a Docker container
./bin/run-test /full/path/to/swath-projector-coverage

Coverage reports are being generate for each build in GitHub, and saved as artifacts.

The tests can also be run outside of the Docker container, for faster checks during development. To do so, first activate the requisite conda environment, which will need requirements (including the test Pip requirements). Then run:

export ENV=test
python -m unittest discover tests

Note - before opening a pull request, all tests should be run in the Docker container environment, to be sure that there isn't something different between the local development environment and the environment in which the Swath Projector will actually run. Additionally, the Docker container invocation will provide pylint checking, to ensure linting errors have not been added during development.

Versioning

As a Harmony service, the Swath Projector is meant to follow semantic version numbers (e.g., major.minor.patch). This version is included in the docker/service_version.txt file. When updating the Swath Projector, the version number contained in that file should be incremented before creating a pull request.

The general rules for which version number to increment are:

• Major: When API changes are made to the service that are not backwards compatible.
• Minor: When functionality is added in a backwards compatible way.
• Patch: Used for backwards compatible bug fixes or performance improvements.

When the Docker image is built, it will be tagged with the semantic version number as stored in docker/service_version.txt.

CI/CD:

The CI/CD for the Swath Projector is contained in GitHub workflows in the .github/workflows directory:

• run_tests.yml - A reusable workflow that builds the service and test Docker images, then runs the Python unit test suite in an instance of the test Docker container.
• run_tests_on_pull_request.yml - Triggered for all PRs against the main branch. It runs the workflow in run_tests.yml to ensure all tests pass for the new code.
• publish_docker_image.yml - Triggered either manually or for commits to the main branch that contain changes to the docker/service_version.txt file.

The publish_docker_image.yml workflow will:

• Run the full unit tests suite, to prevent publication of broken code.
• Extract the semantic version number from docker/service_version.txt.
• Extract the release notes for the most recent version from CHANGELOG.md.
• Create a GitHub release that will also tag the related git commit with the semantic version number.

Before triggering a release, ensure both the docker/service_version.txt and CHANGELOG.md files are updated. The CHANGELOG.md file requires a specific format for a new release, as it looks for the following string to define the newest release of the code (starting at the top of the file).

## vX.Y.Z

pre-commit hooks:

This repository uses pre-commit to enable pre-commit checking the repository for some coding standard best practices. These include:

• Removing trailing whitespaces.
• Removing blank lines at the end of a file.
• JSON files have valid formats.
• ruff Python linting checks.
• black Python code formatting checks.

To enable these checks:

# Install pre-commit Python package as part of test requirements:
pip install -r tests/pip_test_requirements.txt

# Install the git hook scripts:
pre-commit install

# (Optional) Run against all files:
pre-commit run --all-files

When you try to make a new commit locally, pre-commit will automatically run. If any of the hooks detect non-compliance (e.g., trailing whitespace), that hook will state it failed, and also try to fix the issue. You will need to review and git add the changes before you can make a commit.

It is planned to implement additional hooks, possibly including tools such as mypy.

pre-commit.ci is configured such that these same hooks will be automatically run for every pull request.

Get in touch:

You can reach out to the maintainers of this repository via email:

• david.p.auty@nasa.gov
• owen.m.littlejohns@nasa.gov