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A simple question on rotation


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#1 yasmin_bd   Members   -  Reputation: 121

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Posted 24 January 2013 - 01:32 PM

I need some clarification about glRotatef function. I have a rectangular plane with normal ax + by + cz = 0;
I would like to rotate it to align along (0, 1, 0) i.e. Y-axis.
I can find the in-between angle by dot product. Suppose the angle is theta in degree. Now how can I use glRotatef function to rotate the plane so that the new normal to the plane is along (0, 1, 0) vector; Is the following ok?
glRotatef( - theta, a, b, c);
If not, what will be the correct version?



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#2 Brother Bob   Moderators   -  Reputation: 7902

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Posted 24 January 2013 - 01:46 PM

If the plane equaiton is ax+by+cz=0, then the plane's normal is the vector (a,b,c). You want to rotate from one direction to another, so the axis of rotation in this case is the cross product of the plane's normal and the Y-axis.



#3 yasmin_bd   Members   -  Reputation: 121

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Posted 25 January 2013 - 11:02 AM

Thank you, I understand. I need to find the cross product of (ax, by, cz) and (0, y,0) and then use it in glRotatef function.



#4 yasmin_bd   Members   -  Reputation: 121

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Posted 25 January 2013 - 02:50 PM

Could you tell me how to find out the corresponding rotation matrix?



#5 yasmin_bd   Members   -  Reputation: 121

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Posted 25 January 2013 - 05:02 PM

I understand how to convert from axis angle to matrix from wiki.http://en.wikipedia.org/wiki/Rotation_matrix
 






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