Module geoid 

Geoid undulation (geoid height) lookup with bilinear interpolation.

The geoid undulation N is the height of the geoid (mean sea level equipotential surface) above the WGS84 reference ellipsoid, in metres. GNSS positioning yields the ellipsoidal height h; the orthometric height H (height above mean sea level) is

H = h - N

A geoid model is published as a regular latitude/longitude grid of N samples (EGM96, EGM2008, and the national models all ship this way). This module provides:

• GeoidGrid, a regular grid of undulation samples with bilinear interpolation (GeoidGrid::undulation_rad / GeoidGrid::undulation_deg);
• GeoidGrid::from_text, a data-loading hook that parses a simple, documented grid text format so a caller can supply a full EGM grid;
• geoid_undulation, a zero-setup lookup against a small COARSE built-in global grid, plus orthometric_height_m / ellipsoidal_height_m height conversion helpers.

Built-in grid vs. loading a real model

Embedding a full-resolution EGM grid (EGM2008 is a 1-minute, ~2.3 GB grid) is impractical to vendor into the crate, so the built-in grid is a COARSE 30-degree global field. It reproduces the large-scale character of the geoid (the Indian Ocean low, the North Atlantic / New Guinea highs, the polar offsets) and is suitable for tests, sanity checks, and metre-scale fallback, but it is NOT survey-grade. Production code should load a real model through GeoidGrid::from_text (or build a GeoidGrid from any parsed source) and call GeoidGrid::undulation_rad directly.

Structs

GeoidGrid

A regular latitude/longitude grid of geoid undulation samples (metres) with bilinear interpolation.

Enums

GeoidError

Why a geoid grid could not be constructed or parsed.

Functions

ellipsoidal_height_m

Ellipsoidal height h = H + N (metres above the WGS84 ellipsoid) from an orthometric height and a geodetic position in radians, using the built-in grid’s undulation. For a real model, add GeoidGrid::undulation_rad directly.

geoid_undulation

Geoid undulation N (metres above the WGS84 ellipsoid) at a geodetic position in radians, from the COARSE built-in global grid.

orthometric_height_m

Orthometric height H = h - N (metres above mean sea level) from an ellipsoidal height and a geodetic position in radians, using the built-in grid’s undulation. For a real model, subtract GeoidGrid::undulation_rad directly.