'The z direction of the ray.
Positive infinity if the ray points in the positive z direction,
negative infinity if the ray points in the negative z direction,
or 0 if the ray is horizontal.
See Also
xdirection
Examples
>>> from sympy import Point3D, Ray3D
>>> p1, p2, p3 = Point3D(0, 0, 0), Point3D(-1, -1, -1), Point3D(-1, 0, 0)
>>> r1, r2 = Ray3D(p1, p2), Ray3D(p1, p3)
>>> r1.ydirection
-oo
>>> r2.ydirection
0
>>> r2.zdirection
0'

@property
def zdirection(self):

    if (self.p1.z < self.p2.z):
        return S.Infinity
    elif (self.p1.z == self.p2.z):
        return S.Zero
    else:
        return S.NegativeInfinity
