moczarr

Sparse-DGGS xarray reader for morton-hive zarr stores: MOC-declared domains, arithmetic shard paths, lazy dense views.

moczarr opens stores written by zagg under the morton-hive layout convention: a digit tree of self-describing zarr v3 leaves keyed by morton decimal ids, with a static manifest and hierarchical coverage MOCs declaring where data exists — so a reader intersects an area of interest arithmetically instead of listing objects or materializing a global grid.

import moczarr

ds = moczarr.open_hive("s3://bucket/prefix", aoi=["433142"], anonymous=True)

Features

• open_hive() — one call from store root (local path or s3://bucket/prefix) to a lazy xarray.Dataset; AOI covers (packed morton words or decimal strings, mixed orders) and time-window scoping resolve through coverage metadata, not object listings. An AOI over no coverage is a data answer: a schema-correct empty dataset, not an error.
• A MOC-backed lazy index (the default) — the row domain held as a rank-space interval set built from the same coverage arithmetic that selected the leaves; the on-disk cell arrays are never read, and the morton coordinate is fabricated on demand (sel/isel/alignment as interval arithmetic; index_kind="pandas" materializes instead).
• Exact NESTED fabrication — HEALPix NESTED cell_ids derived exactly from the packed morton words ("NESTED is fabricated, never stored").
• Cross-resolution joins — morton truncation makes coarse↔fine work a vectorized lookup: parent_cells for fine→coarse groupby aggregation, join_coarse for the coarse→fine broadcast, no I/O.
• xdggs integration (moczarr[xdggs]) — a registered "morton" grid, so ds.dggs.sel_latlon, cell_boundaries, zoom_to work on any open_hive result.

Docs: espg.github.io/moczarr — quickstart, concepts, API reference, and the example notebook (runnable on binder via the badge above).

Install

pip install moczarr            # core reader
pip install 'moczarr[xdggs]'   # + the ds.dggs accessor integration

Until the first PyPI release lands, install from git:

pip install 'moczarr[xdggs] @ git+https://github.com/espg/moczarr'

Development (uses uv):

uv sync --extra test --extra xdggs
uv run pytest -v

The convention

moczarr is the read side of a convention owned elsewhere: the morton-hive layout and morton decimal ids are specified in the mortie specification, and the coverage tiers, commit-stamp semantics, and reader architecture in zagg's sparse_coverage.md (§4 coverage, §5 reader, §6 xarray extension). Plan and progress: espg/moczarr#1.

License

MIT