MOCPy

MOCPy is a Python library allowing easy creation and manipulation of MOCs (Multi-Order Coverage maps).

MOC is an IVOA standard enabling description of arbitrary sky, time, (or frequency) coverages.

What's in MOCpy?

There is support for one dimensional MOCs:

• Space MOCs. The sky tesselation is based on the HEALPix sky tessellation, it maps regions of the sky into hierarchically grouped cells.
• Time MOCs. The segmentation of the time axis is linear. This is described in the MOC standard since its version 2.0.
• Frequency MOCs. ⚠️ this is not standard yet! The segmentation of the frequency axis is logarithmic. See [this IVOA presentation][https://wiki.ivoa.net/internal/IVOA/InterOpMay2023Apps/FMOC_IVOA_Bologne_Fernique.pdf] for a description.

But also these combinations:

• Space-Time MOCs
• Space-Frequency MOCs

Rendered with MOCpy!

Quick example

from mocpy import MOC
import astropy.units as u

# Create a MOC from a cone
field_of_view = MOC.from_cone(lon=0*u.deg, lat=0*u.deg, radius=10*u.deg, max_depth=7)

# Check if a position is covered
field_of_view.contains_lonlat(0*u.deg, 0*u.deg)  # True

# Combine MOCs with set operations
field_of_view2 = MOC.from_cone(lon=8*u.deg, lat=8*u.deg, radius=5*u.deg, max_depth=7)
coverage = field_of_view | field_of_view2

# Quick preview of the combined field of views
coverage.display_preview()

Other resources

For a command line tool, see the moc-cli.

For more information about MOCPy's Rust core, see the moc crate

Installation

Latest stable version

• from pip pip install mocpy
• from conda conda install -c conda-forge mocpy

Unreleased latest version

To install MOCPy from this repository, make sure you have Python (https://www.python.org/downloads/) and Rust (https://www.rust-lang.org/tools/install) on your machine. Then, run

pip install git+https://github.com/cds-astro/mocpy.git

To run the notebooks

The example notebooks require additional dependencies. They can be installed with

pip install mocpy[notebooks]

Development installation

Contributions are very welcome. To build and test the library, clone this repository, make sure that you've got Rust on your machine (https://www.rust-lang.org/tools/install). Check that the Rust version you have is more recent than the minimal version declared in Cargo.toml under rust-version and do:

pip install pre-commit
pre-commit install
pip install maturin
maturin develop --release

And the library is ready to be edited. After a change on the Rust side, you'll have to do maturin develop --release again. If you only edit the python side, then a pip install . at the root of the repository will suffice.

We use pre-commit to keep consistent style conventions between all of us. This means that your commits will not pass if they require modifications. If this happens, do the required changes, git add the files again and attempt to commit again as usual.

To run the tests, do:

pip install .[dev]
python -m pytest

The tests that require to download remote data from external servers don't run by default. To execute them, do:

python -m pytest --run-remote

To check that the documentation builds. Make sure you have pandoc (https://pandoc.org/installing.html) and do:

pip install .[docs,plots]
cd docs
make clean html

The output will be in docs/_build/html.

For use in pyodide

Wheels that run in pyodide can be downloaded from each github's release for the module.

Other python packages for MOCs

• https://github.com/grahambell/pymoc/