geodesy-wgs84-knowledge-patch

# Geodesy / WGS 84 Knowledge Patch Baseline: WGS 84 (G2139), ITRF2020, and PROJ through 9.3; covers WGS 84 (G2296), ITRF2020-u2024, PROJ 9.4 through 9.8.1, and related implementation details. ## Use this patch Before transforming or comparing coordinates, identify all of the following: - Reference frame or datum realization, not only the label “WGS 84”, “ITRF”, or “ETRS89”. - Coordinate epoch and parameter reference epoch for dynamic frames. - Coordinate type, axis order, units, and dimensionality. - Ellipsoidal, orthometric, dynamic, normal-orthometric, or tidal height semantics. - Required accuracy, area of use, grid availability, and acceptable fallback behavior. Then load the relevant reference below. Preserve explicit directions, signs, epochs, and units when transcribing transformation parameters. ## Reference index | Reference | Topics | | --- | --- | | [Reference frames and datums](references/reference-frames-and-datums.md) | WGS 84 (G2296), ITRF2020-u2024, ETRS89, GPS, GLONASS, Galileo, BeiDou | | [Helmert and datum transformations](references/helmert-and-datum-transformations.md) | PROJ Helmert conventions, kinematic parameters, NGS/HTDP parameters, Molodensky, Molodensky-Badekas, regression transforms | | [Cartesian and local coordinates](references/cartesian-and-local-coordinates.md) | ECEF inverse conversion, fixed-origin ENU, PROJ topocentric operations | | [Ellipsoidal geodesics](references/ellipsoidal-geodesics.md) | Vincenty direct/inverse methods, ant...