whether point is (+-1e-6) on a straight
    line in-between two other points

def pointIsBetween(startP, endP, p):
    """
    whether point is (+-1e-6) on a straight
    line in-between two other points
    """
    return (distancePoint(startP, p) + distancePoint(p, endP)
            - distancePoint(startP, endP) < 1e-6)