Bounday conditions of 3D Random Waypoint Mobility Model

I am working on the 3D RWP mobility model which is an extension of 2D RWP model and facing issues while developing the logic for the points to remain under the specified boundaries in x,y and z coordinates.

I am following this link-

https://in.mathworks.com/matlabcentral/answers/480853-make-random-walk-into-3d

But it is for random walk rather than random waypoint.