def _GetLeastIndex(face, points):
    """Return index of coordinate that is leftmost, lowest in face."""
    bestindex = 0
    bestpos = points.pos[face[0]]
    for i in range(1, len(face)):
        pos = points.pos[face[i]]
        if pos[0] < bestpos[0] or pos[0] == bestpos[0] and pos[1] < bestpos[1]:
            bestindex = i
            bestpos = pos
    return bestindex
