Hi Pawel,

Have a look here: http://euclideanspace.com/maths/algebra/realNormedAlgebra/quaternions/index.htm

It should provide some insight into what quaternions are and how you can use them to rotate or obtain an axis-angle representation.

Cheers,

Tsjerk


On Sun, Nov 24, 2013 at 11:31 PM, Павел Томашевский <crooveck@gmail.com> wrote:
Hi all,

Ok, so today I have to admit that I don't know what quaternions are
but I <probably> will need to use them.
I'm working on PyMOL and Sensable Phantom Omni haptic device
integration using Virtual Reality Peripherial Network (VRPN).

So far I have a nicely working plugin for PyMOL that can retreive
X,Y,Z coordinates and vector of four quaternion values.

My CGO pointer (cone) can smoothly move according to X,Y and Z
changes. Now I need to do some rotations of the pointer. AFAIK
'rotate' function accepts only degree value of rotation around axis.

My question is: is there any build in PyMOL function that accepts four
quaternion values and do rotation (instead of degree for each axis)?

If not: do you have any simple hint or math formulas for me :) to
calculate angles for rotation of CGO out of four quaternion value?

Cheers
Pawel 'crooveck' Tomaszewski

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--
Tsjerk A. Wassenaar, Ph.D.