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Trying to simulate 3D Rotation as Office 2007

Hi,

I’m trying to simulate the 3D rotation feature of Office 2007. I understand X, Y, and Z rotation but I cannot figure out how Perspective Angle works. In Perspective angle box I can enter an angle number from 0 to 120 degrees. My question is what is the math behind it? I mean, suppose you rotate a rectangle at 20 degrees in X axis and then set a perspective angle of 45 degrees. So, how that rectangle is transformed into a trapezoid i.e. what is the math used to translate the original 4 points of the rectangle into the 4 points of the trapezoid?

Thanks in advance,
Gabriel
Wednesday, May 16, 2007
 
 
Learn about polar coordinates first and translating to/from cartessian coordinates. It will probably become much clearer.

If you still have questions about how the rotation is done in polar coordinates, re-ask the question.
Adrian
Wednesday, May 16, 2007
 
 
Check out the variable 'w', maybe wikipedia has an article on transformations (I'm too lazy to type in anything).

If you want decent looking changes between orientations, look up 'quaternion'.
old.fart
Wednesday, May 16, 2007
 
 
old.fart
Wednesday, May 16, 2007
 
 
Google "perspective transformations".
A. Nonymous
Wednesday, May 16, 2007
 
 
Also google "view matrix" -- you can first concatenate the rotation, translation and projection transformations into one matrix, then multiply that by each vertex in your object to determine the screen coordinate.
John
Wednesday, May 16, 2007
 
 
(Old thread, I know, but I don't check back here that often.)

Never seen that feature, so I can't say for certain, but given the range that you mentioned, I'd guess that it's actually just a field-of-view angle.  In most 3d systems, the field-of-view angle is the size of the angle taken in by the width of the screen or the image.  Usually larger angles give you more perspective distortion and show more of a scene.  Smaller angles give much less perspective distortion and a more telephoto like effect.

For something like rotating a quad, you'll probably just end up with it  controlling a combination of how far back (into the screen) you translate the quad and how much you scale in 2d to compensate. There's typically just a tan() call when I implement it.
Boojum
Monday, May 28, 2007
 
 

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