http://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation
Does this help?
Bob
Miguel wrote:
I'm volunteering, but I need a very specific goal. Exactly what is
being
asked? Are we trying to do smooth animation or a sudden jump? Does the current
user-influenced rotation status need to be a starting point? (Miguel, have you
An elegant and smooth rotation from the current position is ideal. A
suddent jump is a good alternative to the current 'no option' status.
Certainly when we implement it the rendering will be smooth. It seems to me that we should allow the user to specify either a time or a rotation rate in degrees per second.
Here is the way that I have been thinking about it ...
We have a transformation matrix that represents the current rotation state, A.
We need to go from the transformation matrix in state A to the transformation matrix in state B.
Therefore, what matrix operation do we perform on A to get to B
A * ? = B
I don't know what this is called ...
Q: What is this called?
Once we get this matrix, then I can convert it to an AxisAngle rotation. This will tell us what axis to rotate about and how many degrees to rotate. At that point the animation is easy.
Now, let's look for a simple case. Let's say that we want to be able to rotate from the current position (after some arbitrary set of rotations), back to the startup state. When the molecular model is first loaded the transformation matrix is the identity matrix, I. So we are saying
A * ? = I
In this case I think that we just need to calculate the inverse of A ...
Q: Is that correct?
The Java3D vecmath library will calculate the inverse of a matrix. So maybe this part isn't that difficult.
Q: In the more general case, what are the operations required to calculate A * ? = B ?
I have more questions, but that is enough to get us started.
Miguel
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