Angle of x-axis relative to ground (theta)

    Args
    ----
    ax: ndarray
        x-axis acceleration values
    ay: ndarray
        y-axis acceleration values
    az: ndarray
        z-axis acceleration values

    Returns
    -------
    pitch: ndarray
        Pitch angle in radians

def pitch(ax, ay, az):
    '''Angle of x-axis relative to ground (theta)

    Args
    ----
    ax: ndarray
        x-axis acceleration values
    ay: ndarray
        y-axis acceleration values
    az: ndarray
        z-axis acceleration values

    Returns
    -------
    pitch: ndarray
        Pitch angle in radians
    '''
    import numpy
    # arctan2 not needed here to cover all quadrants, just for consistency
    return numpy.arctan(ax, numpy.sqrt(ay**2+az**2))