Project 3D Points to 2D Image with Asus Xtion Pro

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Hi!

I am new here and I had quite a urgent question:

I have depth image from a Asus Xtion Pro sensor and I wanted to draw a 3D cuboid in it. This cuboid is drawn around every person entering the room covering it's complete body so it must align to the floor.

What I have found out till now is that I need a bunch of parameters wich I normally would get by calibrating the camera, if I had a conventional one. Now I am trying to use the "SolvePnP" Method with custom "cheesboard"-points to get the translation and rotation vector I need for drawing the cuboid. Has anyone had a similar experience?