I have a rectangle i am rotating in 3d on multiple axis. i am trying to calculate the 2d height of the rectangle and im quite lost.

For example, if i rotate the rectangle on the x axis so the top of the rectangle comes forward and the bottom moves back. i can calculate the height of this fine.

But then i rotate it on the y axis so the left side of the rect moves to the right and the right hand side moves left.

Whats the total height from the bottom left corner to the top right corner when rotated on 2 axis?

Its for an orthographic view of the object where you show the front, top and side views of the 3d object.

Any clue how i can calculate this?

Cheers =)