# Authoritative sources

- Last verified: 2026-07-19
- Review cadence: every 6 months
- Refresh triggers: GSTools, PyKrige, or scikit-gstat major release

## Canonical sources

- [GSTools documentation](https://geostat-framework.readthedocs.io/projects/gstools/en/stable/) — covariance models, variograms, and kriging workflows.
- [PyKrige documentation](https://geostat-framework.readthedocs.io/projects/pykrige/en/stable/) — ordinary, universal, and regression kriging APIs.
- [scikit-gstat documentation](https://scikit-gstat.readthedocs.io/en/latest/) — empirical variogram estimation and diagnostics.

Treat package defaults as implementation details, not methodological authority. Record estimator, model, fitting method, transform, distance units, and package version with every result.