def to3(pnts):
    """
    Convert homogeneous coordinates to plain 3D coordinates.

    It scales the x, y and z values by the w value.

    Aruments:
        pnts: A sequence of 4-tuples (x,y,z,w)

    Returns:
        A list of 3-tuples (x,y,z)
    """
    return [(p[0] / p[3], p[1] / p[3], p[2] / p[3]) for p in pnts]