def track_point(start, direction, z):
    """
    This function returns the segment coordinates for a point along the `z` coordinate

    Args:
        start (tuple): start coordinates
        direction (tuple): direction coordinates
        z (float): `z` coordinate corresponding to the `x`, `y` coordinates

    Returns:
        tuple: the (x,y) pair of coordinates for the segment at `z`
    """
    l = (z - start[2]) / direction[2]
    xl = start[0] + l * direction[0]
    yl = start[1] + l * direction[1]

    return xl, yl