mortie 0.5.0

Morton numbering and indexing for healpix grids

mortie

Mortie is a library for applying morton indexing to healpix grids. Morton numbering (also called z-ordering) facilitates several geospatial operators such as buffering and neighborhood look-ups, and can generally be thought of as a type of geohashing.

This particular implementation focuses on hierarchical healpix maps, and is mostly inspired from this paper.

Performance

Mortie uses Rust-accelerated morton indexing functions for high performance, with an automatic fallback to pure Python if Rust is unavailable. The Rust implementation provides dramatic speedups:

Dataset Size	Rust	Pure Python	Speedup
1,000 values	1.93 ms	4.14 ms	2.1x
100,000 values	1.85 ms	410.59 ms	222x
1.2M coordinates	102.51 ms	5.1 sec	50x

Pre-built wheels are available for Linux, macOS, and Windows. If a wheel is unavailable for your platform, mortie will automatically use the pure Python fallback.

Installation

pip install mortie

For development builds with Rust, see BUILDING.md.

TODO:

• add paper reference
• add funding information
• add tests
• remove / prune dead code
• add example(s)
• fix north / south bug
• remove numba dependency
• update documentation
• publish to pypi

Dependencies are numpy and healpy. The Rust-accelerated functions are optional - if unavailable, mortie will automatically fall back to a pure Python implementation. Although not a dependency, there are several functions that have been written to interface with the vaex project.

Funding

Initial funding of this work was supported by the ICESat-2 project science office, at the Laboratory for Cryospheric Sciences (NASA Goddard, Section 615).

References

[1] Youngren, Robert W., and Mikel D. Petty. "A multi-resolution HEALPix data structure for spherically mapped point data." Heliyon 3.6 (2017): e00332. doi: 10.1016/j.heliyon.2017.e00332