"""Constants used in several places throughout the GPS package."""

__all__ = ("WGS84", "GPS_PI", "SPEED_OF_LIGHT_M_S", "SPEED_OF_LIGHT_KM_S")


class WGS84:
    """WGS84 ellipsoid model parameters for Earth."""

    ####################################################################
    # Defining parameters of WGS84 come first

    EQUATORIAL_RADIUS_IN_METERS: float = 6378137.0
    """Equatorial radius of Earth in the WGS ellipsoid model"""

    INVERSE_FLATTENING: float = 298.257223563
    """Inverse flattening of Earth in the WGS ellipsoid model"""

    GRAVITATIONAL_CONSTANT_TIMES_MASS: float = 3.986005e14
    """Gravitational constant times Earth's mass"""

    ROTATION_RATE_IN_RADIANS_PER_SEC: float = 7.2921151467e-5
    """Earth's rotation rate [rad/sec]"""

    ####################################################################
    # Non-defining parameters of WGS84 are below

    FLATTENING = 1.0 / INVERSE_FLATTENING
    """Flattening of Earth in the WGS ellipsoid model"""

    ECCENTRICITY = (FLATTENING * (2 - FLATTENING)) ** 0.5
    """Eccentricity of Earth in the WGS ellipsoid model"""

    ECCENTRICITY_SQUARED = ECCENTRICITY**2
    """Square of the eccentricity of Earth in the WGS ellipsoid model"""

    POLAR_RADIUS_IN_METERS = EQUATORIAL_RADIUS_IN_METERS * (1 - FLATTENING)
    """Polar radius of Earth in the WGS ellipsoid model"""

    MEAN_RADIUS_IN_METERS = (
        2 * EQUATORIAL_RADIUS_IN_METERS + POLAR_RADIUS_IN_METERS
    ) / 3
    """Mean radius of Earth in the WGS ellipsoid model, as defined by IUGG"""


GPS_PI = 3.1415926535898
"""Value of pi used in some GPS-specific calculations."""

SPEED_OF_LIGHT_KM_S = 299792.458
"""Speed of light in km/s"""

SPEED_OF_LIGHT_M_S = 299792458.0
"""Speed of light in m/s"""