pyslga

Cached SLGA soil-property windows for Australia — download once per chunk, never twice. The Soil and Landscape Grid of Australia provides national ~90 m grids of soil properties (clay, sand, silt, pH, bulk density, AWC, …) at six standard depths, served as one COG per attribute × depth on the TERN datastore. Every pixel this machine ever downloads lands in one sparse, chunk-indexed store, so repeat requests, overlapping AOIs and new depth slices reuse everything already fetched. Part of the Borevitz Lab ecosystem.

How it works

{data_root}/slga_store/
├── index.db      # SQLite: layer metadata + populated chunks
└── slga.zarr/
    ├── CLY_005_015   # one sparse national array per attribute × depth
    └── SND_005_015 ...

• At a layer's first contact, its COG filename is resolved from the datastore listing (each attribute has its own release date, so names can't be hardcoded) and its grid — transform, shape, nodata — is read from the COG and recorded. Everything after that is offline arithmetic.
• Any bbox maps deterministically to a set of 1200 × 1200-px chunks on the layer's native grid. Store.get_ds(bbox) diffs them against the ledger and downloads only the missing chunks, each as one integer-aligned windowed read — no resampling, ever.
• Soil properties are time-invariant: no time axis, no dates.
• Pixel reads require a TERN API key (listings are public) — set tern_api_key in ~/.config/Troi.json, TROI_TERN_KEY, or pass api_key= per call. Keys are free from https://account.tern.org.au/.

Usage

The core API is troi-agnostic — just a bbox:

from pyslga.store import Store

store = Store()
bbox = [148.36265, -33.52606, 148.38265, -33.50606]  # [W, S, E, N]

ds = store.get_ds(bbox)   # texture triple Clay/Sand/Silt at 5-15cm
ds = store.get_ds(bbox, attributes=('Clay', 'pH_Water', 'Bulk_Density'),
                  depths=('0-5cm', '5-15cm', '15-30cm'))
ds['Clay_5-15cm']         # (lat, lon) DataArray

store.fill(bbox)          # → 0: already local

16 attributes × 6 depths are available — see pyslga.slga.SLGA for the catalog.

Pipelines that speak the shared troi.troi.Troi use the adapters (dates on the troi are ignored):

ds = store.get_ds_troi(troi)

download_slga_soils(troi) remains as a thin wrapper.

Performance

Live measurements against TERN — a ~2 × 2 km AOI (one chunk = 1200 × 1200 px ≈ 100 × 100 km at 90 m):

Store footprint: ~5 MB for six layer-chunks (~10 000 km² each of Clay/Sand/Silt at two depths). Absolute times vary with network and TERN load; the zeros are the point — they are ledger lookups, no network involved.

Install

pip

pip install git+https://github.com/thestochasticman/pyslga.git

Dependencies (the troi core included, pulled from GitHub) are declared in pyproject.toml and installed automatically.

From source

git clone https://github.com/thestochasticman/pyslga.git
cd pyslga
pip install -e .

Package design (shared across the lab's packages — no inheritance, composition only):

• Troi (from troi) — identity: what region.
• SLGA (pyslga.slga) — config: endpoint, attribute/depth catalogs.
• Paths (pyslga.paths) — derived locations of the store for a given Config.
• grid — chunk math parameterised by each layer's native grid (pure, offline-testable).
• Store (pyslga.store) — ties them together.

Test

# offline (pure math + synthetic store):
python pyslga/grid.py     # True
python pyslga/paths.py    # True
python pyslga/store.py    # True

# live (small real reads from TERN — needs tern_api_key):
python pyslga/download_slga.py  # True