# Posts tagged ‘Trigonometry’

I posted this at cgtalk

Has anyone though of using VCK with a transposed arc length method to get rotations about the elbow? Basically VCK ‘vector coupled ik’ is an ik chain driven by the vector magnitude to positioning the goal whilst having standard rotation for general fk, it basically allows you to break the ik and add nice arcs to the animation – the problem i see with it is you cant drive about the elbow. But what if we use a transposed arch length method, which would ontop drive the general rotation and the magnitude we could get rotation about the elbow- this could even have its own fk controller driving additively over the top i think -you need just a few variables such as bone length, as you drive it as an additive to the main control i.e a layer over the top.

I now must go to bed.

I was reading up on the stunning work Crytek are doing in Germany – they mention ccd-ik as one approach to parametric animation. CCDIK or ‘Cyclic-Coordynate Descent Inverse kinematics’ is a simple non-analytical approach to IK that doesnt envolve trigonometry, locking bone chains to two or even a deterministic ik goal – the goal with this system can be anywhere, and so can the number of bones in the chain and where the ik starts and ends from.

I’ll look into this more – i have a funny idea that CAT tools use the same approach to FIK.

Edit:  I dont know how the swivel/pole vector is handled, but I have some ideas.

I thought about an idea for unifying an fk/ik system today – using a single fk chain driven by a detached wrist to define a hypotenuse, to make it act like IK. And driving the same wrist with weak node referencing, and storing two matrix3 values driving its transform space so it stays glued to the end of the elbow joint. Rotation would use the same method.

So you would move the wrist, and in doing so define the 3 lengths needed for ik solution (2 of the lengths are constant unless you introduce stretching). And when you rotate the bones – on another float_list (bezier controller) you drive the transform positional space of the wrist, keeping it glues to the end of the elbow.

Weak referencing could also be used for gluing the knee control to the knee, and also a control at the elbow to break it, stretch it etc.

Some issues maybe doubling of transforms, plus controlling the elbow. Also pulling the wrist too far from the the ik solution – this i think could be fixed.