def sphere_to_plane_car(az0, el0, az, el):
    """Project sphere to plane using plate carree (CAR) projection.

    The target point can be anywhere on the sphere. The output (x, y)
    coordinates are likewise unrestricted.

    Please read the module documentation for the interpretation of the input
    parameters and return values.

    Parameters
    ----------
    az0 : float or array
        Azimuth / right ascension / longitude of reference point(s), in radians
    el0 : float or array
        Elevation / declination / latitude of reference point(s), in radians
    az : float or array
        Azimuth / right ascension / longitude of target point(s), in radians
    el : float or array
        Elevation / declination / latitude of target point(s), in radians

    Returns
    -------
    x : float or array
        Azimuth-like coordinate(s) on plane, in radians
    y : float or array
        Elevation-like coordinate(s) on plane, in radians

    """
    return az - az0, el - el0