def vector(p1, p2):
return np.subtract(p1[COLS.XYZ], p2[COLS.XYZ])<EOL>
compute vector between two 3D points

    Args:
        p1, p2: indexable objects with
        indices 0, 1, 2 corresponding to 3D cartesian coordinates.

    Returns:
        3-vector from p1 - p2