# Question about slerping quaternions (insert joke here)

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Lets say I have two object Obj1 and Obj2 and I want the orientation of Obj1 to become the orientation of Obj2. Both objects have orientations represented as quaternions and in order for me to orient Obj1 I slerp its orientation using the orientation of Obj2 as the destination for the slerp. My question is, since slerp generates intermediate results between two orientations do I have to do something like (in pseudo code):
while Obj1->orien != Obj2->orien
slerp(Obj->orien, Obj2->orien, t) // objects passed by reference
loop


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The parameter t is an interpolant, not a time value. If you feed t=0 into slerp, you'll get Q1, if you feed t=1 in, you'll get Q2. Values of t in between 0 and 1 will give you a quaternion in between Q1 and Q2. Outside 0 and 1... not well-defined.

If you want to increment t from 0 to 1 using a timestep, you could do something like:
const kMaxSlerpTimetotalSlerpTime = 0while Obj1->orien != Obj2->orien && totalSlerpTime < kMaxSlerpTime     totalSlerpTime = totalSlerpTime + dt     t = Clamp(totalSlerpTime/kMaxSlerpTime, 0, 1)     slerp(Obj1->orien, Obj2->orien, t) loop

P.S. I may have misunderstood the question.

[Edited by - jvsquare on August 10, 2006 10:42:01 AM]

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Something that might affect your choice of algorithm is whether the target orientation can change while the other orientation is attempting to match it.

If not, you can simply slerp between the original orientation and the target orientation using the appropriate value of t. t should progress from 0 to 1, with the speed of progression depending on how quickly you want the first orientation to match the second.

Note that with this approach there's no need to test the orientations for equality; when t reaches 1, you will have reached your goal.

If the target orientation is also changing, a different approach may be required (perhaps you could clarify whether or not this is the case).

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