Principal vanishing point write respect to y-axis
By the 2nd Row of the matrix as in Equation, the principal vanishing point w.r.t y-axis will as:
(0, 5/√2, 0, 1/√2) in homogeneous system is:
The vanishing point in Cartesian system as:
(0, (5/√2)/( 1/√2), 0)