apsis-rs/crates/physics/apsis-geodesy/tests/geodetic.rs

//! Tests for geodetic and Earth-centered, Earth-fixed conversions.

use apsis_geodesy::{Ecef, Geodetic, WGS84};
use apsis_math::Vec3;

/// Tolerance for position comparisons, in meters.
const POSITION_TOL: f64 = 1e-4;

/// Tolerance for latitude and longitude comparisons, in radians.
///
/// One microdegree is about 1.1e-8 radians, or roughly a centimeter on the
/// Earth's surface.
const ANGLE_TOL: f64 = 1e-11;

#[test]
fn equatorial_point_lies_on_the_semi_major_axis() {
    let point = Geodetic::new(0.0, 0.0, 0.0).to_ecef(WGS84);
    assert!((point.position().x - WGS84.semi_major_axis()).abs() < POSITION_TOL);
    assert!(point.position().y.abs() < POSITION_TOL);
    assert!(point.position().z.abs() < POSITION_TOL);
}

#[test]
fn pole_lies_on_the_semi_minor_axis() {
    let point = Geodetic::new(core::f64::consts::FRAC_PI_2, 0.0, 0.0).to_ecef(WGS84);
    assert!(point.position().x.abs() < POSITION_TOL);
    assert!(point.position().y.abs() < POSITION_TOL);
    assert!((point.position().z - WGS84.semi_minor_axis()).abs() < POSITION_TOL);
}

#[test]
fn longitude_quarter_turn_places_the_point_on_the_second_axis() {
    let point = Geodetic::new(0.0, core::f64::consts::FRAC_PI_2, 0.0).to_ecef(WGS84);
    assert!(point.position().x.abs() < POSITION_TOL);
    assert!((point.position().y - WGS84.semi_major_axis()).abs() < POSITION_TOL);
}

#[test]
fn height_moves_the_point_along_the_ellipsoid_normal() {
    let surface = Geodetic::new(0.6, 0.3, 0.0).to_ecef(WGS84);
    let elevated = Geodetic::new(0.6, 0.3, 500.0).to_ecef(WGS84);
    assert!((surface.position().distance(elevated.position()) - 500.0).abs() < POSITION_TOL);
    // The normal at a non-polar latitude is not vertical, so the height
    // changes the horizontal components as well as the third one.
    assert!(elevated.position().x > surface.position().x);
}

#[test]
fn conversion_round_trips_over_a_global_grid() {
    for latitude_degrees in [-89.9_f64, -60.0, -45.0, 0.0, 30.0, 45.0, 60.0, 89.9] {
        for longitude_degrees in [-179.0_f64, -90.0, 0.0, 45.0, 90.0, 179.0] {
            for height in [-1_000.0_f64, 0.0, 1_000.0, 35_786_000.0] {
                let original = Geodetic::new(
                    latitude_degrees.to_radians(),
                    longitude_degrees.to_radians(),
                    height,
                );
                let ecef = original.to_ecef(WGS84);
                let recovered = ecef
                    .to_geodetic(WGS84)
                    .expect("off-axis points have a longitude");
                assert!(
                    (recovered.latitude - original.latitude).abs() < ANGLE_TOL,
                    "latitude mismatch at {latitude_degrees}, {longitude_degrees}, {height}"
                );
                assert!(
                    (recovered.longitude - original.longitude).abs() < ANGLE_TOL,
                    "longitude mismatch at {latitude_degrees}, {longitude_degrees}, {height}"
                );
                assert!(
                    (recovered.height - original.height).abs() < POSITION_TOL,
                    "height mismatch at {latitude_degrees}, {longitude_degrees}, {height}: {} vs {}",
                    recovered.height,
                    original.height
                );
            }
        }
    }
}

#[test]
fn round_trip_preserves_the_cartesian_position() {
    let original = Geodetic::new(0.921, -1.234, 12_345.0).to_ecef(WGS84);
    let recovered = original
        .to_geodetic(WGS84)
        .expect("off-axis points have a longitude")
        .to_ecef(WGS84);
    assert!(original.position().distance(recovered.position()) < POSITION_TOL);
}

#[test]
fn polar_axis_has_no_defined_longitude() {
    let on_axis = Ecef::new(Vec3::new(0.0, 0.0, WGS84.semi_minor_axis()));
    assert_eq!(on_axis.to_geodetic(WGS84), None);
    // The origin is also on the axis.
    assert_eq!(Ecef::new(Vec3::ZERO).to_geodetic(WGS84), None);
}

#[test]
fn non_finite_positions_are_rejected() {
    let invalid = Ecef::new(Vec3::new(f64::NAN, 0.0, 6_000_000.0));
    assert_eq!(invalid.to_geodetic(WGS84), None);
    let infinite = Ecef::new(Vec3::new(f64::INFINITY, 0.0, 0.0));
    assert_eq!(infinite.to_geodetic(WGS84), None);
}

#[test]
fn known_point_matches_an_independent_computation() {
    // Latitude 37.5 degrees north, longitude 121.333333... degrees west, at
    // zero height, evaluated with the defining WGS 84 parameters in
    // extended precision.
    let point = Geodetic::new(
        37.5_f64.to_radians(),
        -121.333_333_333_333_33_f64.to_radians(),
        0.0,
    )
    .to_ecef(WGS84);
    assert!(
        (point.position().x + 2_634_612.181_141_605_6).abs() < 1e-6,
        "x = {}",
        point.position().x
    );
    assert!(
        (point.position().y + 4_327_502.253_728_065).abs() < 1e-6,
        "y = {}",
        point.position().y
    );
    assert!(
        (point.position().z - 3_861_564.098_809_606_4).abs() < 1e-6,
        "z = {}",
        point.position().z
    );
}

#[test]
fn validity_is_reported() {
    assert!(Geodetic::new(0.5, 0.5, 100.0).is_valid());
    assert!(Geodetic::new(core::f64::consts::FRAC_PI_2, 0.0, 0.0).is_valid());
    assert!(!Geodetic::new(2.0, 0.0, 0.0).is_valid());
    assert!(!Geodetic::new(0.0, 4.0, 0.0).is_valid());
    assert!(!Geodetic::new(0.0, 0.0, f64::NAN).is_valid());
}

#[test]
fn ecef_wrapper_exposes_its_vector() {
    let vector = Vec3::new(1.0, 2.0, 3.0);
    let ecef = Ecef::new(vector);
    assert_eq!(ecef.position(), vector);
    assert_eq!(ecef, Ecef(vector));
}