zagg - Multi-resolution Aggregation

Aggregate point observations to multi-resolution grids using HEALPix spatial indexing and serverless compute.

Overview

zagg aggregates sparse point data (e.g., ICESat-2 ATL06 elevation measurements) to gridded products using HEALPix/morton spatial indexing. Processing runs in parallel on AWS Lambda — each worker handles one spatial cell independently, writing to a shared Zarr v3 store following the DGGS convention.

Features

• Pre-computed granule catalogs — query CMR once, process many times
• Morton-based spatial indexing — HEALPix nested scheme for hierarchical grids
• Massive parallelism — tested with up to 1,700 concurrent Lambda workers
• Direct S3 access — h5coro reads HDF5 via byte-range requests, no downloads
• Cost-effective — $0.006/cell ($2 per full Antarctica run on ARM64)

End-to-End Workflow

Step 1: Build a Granule Catalog

Query NASA's CMR-STAC to build a shard map of grid cells to granules. The grid comes from the same pipeline config the aggregator uses (--config), so the shard map can't be built against a different grid than the run.

# Install the catalog extra (STAC fetch + shard-map build). The geometry
# backend defaults to `auto`: exact-S2 spherely if its fork is installed (used
# for all grids), else mortie (HEALPix MOC); rectilinear grids require spherely.
pip install 'zagg[catalog]'

# Optional: the exact-S2 spherely SpatialIndex backend is a fork not on PyPI
# (benbovy/spherely#118) — install it separately (pick the wheel for your
# python/platform from the release assets):
# pip install "spherely @ https://github.com/espg/spherely/releases/download/v0.1.1-spatialindex/spherely-0.1.1+spatialindex-cp312-cp312-manylinux_2_28_x86_64.whl"

# ICESat-2 convenience — cycle number computes dates automatically:
uv run python -m zagg.catalog --config atl06.yaml --short-name ATL06 --cycle 22 \
    --polygon my_region.geojson

# General — explicit date range and a bbox:
uv run python -m zagg.catalog \
    --config atl06.yaml --short-name ATL06 \
    --start-date 2024-01-06 --end-date 2024-04-07 \
    --polygon my_region.geojson

--polygon drives both the CMR query bbox and the coverage mask; --bbox gives the query box directly. Each granule record keeps both its S3 and HTTPS hrefs; the run picks one via data_source.driver.

Output: shardmap_ATL06_2024-01-06_2024-04-07.json

See Catalog API for full options.

Step 2: Deploy the Lambda Function

Quick standup (CloudFormation). Stand up the whole backend — IAM role, dependency layer, and function — in your own AWS account from the pre-built release zips:

OUTPUT_BUCKET=my-results-bucket bash deployment/aws/stand_up.sh
# don't have the results bucket yet? add CREATE_BUCKET=true
# deploying outside us-west-2? add REGION=... STAGING_BUCKET=a-bucket-you-own-in-that-region

In us-west-2 the stack reads the Lambda code straight from the public source.coop mirror — no staging bucket of your own needed. Outside us-west-2, CloudFormation requires the code in a same-region bucket, so pass a STAGING_BUCKET you own and the zips are copied there from the mirror first. Deploys deployment/aws/template.yaml; the artifacts are keyed by zagg minor version (derive from your install, or pin with LAMBDA_VERSION=0.N). Override ARCH for x86_64.

Build from source (maintainers, or to customize the layer):

# Build the function package
bash deployment/aws/build_function.sh

# Build the dependency layer (ARM64)
bash deployment/aws/build_layer.sh arm64

# Deploy (updates an already-deployed function from CI artifacts)
bash deployment/aws/deploy.sh

See Lambda Deployment and ARM64 Build Guide.

Step 3: Run Processing

Processing reads a pipeline config YAML (data source, aggregation, output store) and a granule catalog. Run locally or dispatch to Lambda.

# Local processing (write to local Zarr):
uv run python -m zagg --config atl06.yaml --catalog catalog.json --store ./output.zarr

# Local processing (write to S3):
uv run python -m zagg --config atl06.yaml --catalog catalog.json --store s3://bucket/output.zarr

# Lambda dispatch (requires deployed Lambda function):
uv run python deployment/aws/invoke_lambda.py \
    --config atl06.yaml --catalog catalog.json

# Test with a few cells:
uv run python -m zagg --config atl06.yaml --catalog catalog.json --max-cells 5

# Dry run:
uv run python -m zagg --config atl06.yaml --catalog catalog.json --dry-run

The store path and output grid parameters are defined in the YAML config (output.store, output.grid.child_order) and can be overridden via --store on the command line.

Step 4: Visualize Results

The output Zarr is a public DGGS dataset. The included notebook rasterizes HEALPix cells to a polar stereographic grid for fast rendering with imshow.

uv run jupyter notebook notebooks/rasterized_zarr.ipynb

Adjust GRID_SPACING in the notebook to control output resolution.

Example Notebooks

The notebooks under notebooks/ run on Binder — no install, no credentials. They install zagg[analysis] via the .binder/ conda config and read only synthetic in-notebook data or the anonymous, public source.coop benchmark store.

Notebook	What it shows	Binder
custom_aggregations.ipynb	Config-driven aggregation API on synthetic data
rasterized_zarr.ipynb	Rasterize the published HEALPix store to an 8 km polar-stereo grid
jupyterhub_example.ipynb	Drive the API from a science hub; read & visualize a published result
cryocloud_example.ipynb	End-to-end ISMIP6 read + AWS Lambda fan-out on CryoCloud	not Binder-runnable (needs live AWS + Earthdata credentials)

cryocloud_example.ipynb is the only Lambda demo; it dispatches to a deployed AWS Lambda and reads private-account S3 via the CryoCloud IRSA role, so it cannot run on Binder.

Project Structure

zagg/
├── src/zagg/              # Main package (cloud-agnostic)
│   ├── __main__.py        # Local processing runner (python -m zagg)
│   ├── config.py          # YAML pipeline configuration
│   ├── processing.py      # Core aggregation pipeline
│   ├── catalog.py         # CMR query + catalog building
│   ├── schema.py          # Output schema + Zarr template
│   ├── store.py           # Store factory (local or S3)
│   ├── auth.py            # NASA Earthdata authentication
│   └── configs/           # Built-in pipeline configs (atl06.yaml)
├── deployment/            # Cloud-specific deployment
│   └── aws/               # Lambda handler, orchestrator, build scripts
├── notebooks/             # Visualization
├── docs/                  # Documentation
└── tests/                 # Test suite

Documentation

• Architecture — design philosophy, end-to-end flow diagram, key decisions
• Schema — aggregation dispatch, extending with new statistics
• API Reference — catalog, processing, schema, auth modules
• Lambda Deployment — AWS setup and production use
• ARM64 Build Guide — building Lambda layers for ARM64

Development

# Install
uv sync --all-groups

# Run tests
uv run pytest

# Lint
uv run ruff check src/

Requires Python >= 3.12, uv, AWS credentials (for Lambda), and a NASA Earthdata account (for data access).

Performance

Metric	Value
Execution time	2–3 min average per cell
Memory	2 GB configured, 1–1.5 GB typical
Throughput	Tested with up to 1,700 concurrent workers
Cost	$0.006/cell ($2 per full Antarctica run on ARM64)

License

MIT — see LICENSE file.