[CSC 315] Re: Exam 2 Questions

[Andrew J. Pounds]

David Thomas wrote:
> Hi Dr. Pounds.
>
> So, I'm moving along in the test, and I have a question about #2 part (c). You 
> want us to rotate 45 degrees (counterclockwise, I assume) about the Z-Axis, 
> then rotate by a 30 degree clockwise rotation "about the rotation point B 
> within the xy-plane". Do you want the second rotation to be about the new 
> location of B after the first rotation? So, is the rotation point B being 
> rotated as well? In other words, are we rotating about the point B=(5,3,0) or 
> about the point B'=(sqrt(2),4*sqrt(2),0)? I hope that makes sense.
>   
Yes -- B will have to move too.
> Also, another quick one: on part (d), if we use OpenGL routines, can we pass 
> in the old values to drawArrow() and assume that drawArrow() will use the 
> current ModelView matrix to translate as it draws the arrow? In other words, 
> must we update x0,y0,z0,x1,y1,z1 with their new positions before calling 
> drawArrow() or can we assume that OpenGL will do that for us under the hood?
>
>   
Yes -- the coordinates of the beginning and ending point of the vector 
will have to be updated before you call
drawArrow.  Make this easy on yourself -- don't start playing with the 
modelview and transformation matrices yet.

> Sorry for my confusion, and thanks for your help!
>
> ~David
>   


-- 
Andrew J. Pounds, Ph.D.  (pounds at theochem.mercer.edu)
Associate Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627