3D rotation question

[Keith W. <kw...@cs...>]

I hope someone can help with this.  I have a 3D object which is a single 
flat square, two triangles.  The square is initially positioned 
"horizontal", parallel to the ground plane.  The X and Z axes are aligned 
with the axes of the square incidently.

I want to alter the orientation by first pitching the square some, so it 
becomes a ramp with two sides, and then rotating the ramp around a 
vertical axis so I can face the ramp anyway I want (or alternatively by 
rotating the square in some direction and then pitch the square into a 
ramp in the new direction).  The problem of course is that I can't yaw and 
then pitch or pitch and then yaw, because in either case, the first 
rotation changes the axes so the second rotation doesn't do what I 
want it to do.  How do I maintain or regain the original axes?

Can I pitch the square and then regain the vertical axis so I can yaw the 
ramp to face any direction I want?  How do I do this?

Thanks.

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Keith Wiley         kw...@cs...         http://www.unm.edu/~keithw

"Yet mark his perfect self-contentment, and hence learn his lesson,
that to be self-contented is to be vile and ignorant, and that to
aspire is better than to be blindly and impotently happy."
                                            --  Edwin A. Abbott, Flatland
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