Thanks for kind support @lassoan

Found this, after some research

"Similarly we can also calculate backwards and find the intantanous axis of rotation at some distance

−

⃗

r

from any point if we know the linear velocity of the point and the angular velocity. This is given by:

[\begin{equation} \label{eq:2} -\vec{r}= \frac{\vec{\omega} \times \vec{v}_P }{ \vec{\omega}\cdot\vec{\omega} } \end{equation}]

Thus if know the position of a point

⃗

r

P

, its linear velocity

⃗

v

P

we can find closest point

⃗

r

C

on the rotation axis as:

[\vec{r}_C = \vec{r}_P - \vec{r} = \vec{r}_P + \frac{\vec{\omega}\times\vec{v}_P}{\vec{\omega}\cdot\vec{\omega} }]

Script

```
AnyKinRotational Rotational ={
AngVelOnOff = On;
AnyRefFrame& Ref1= .ReferenceFrame;
};
AnyKinLinear Linear ={
Ref=-1;
AnyRefFrame& Ref1= .ReferenceFrame;
};
/// Direction of the instantaneous axis of rotation
AnyVec3 e_iaor = Rotational.Vel/vnorm(Rotational.Vel)
/// The point on the rotation axis closest to ReferenceFrame origin
AnyVec3 r_iaor = Linear.Pos + cross(Rotational.Vel, Linear.Vel)/(vnorm(Rotational.Vel)^2);
```

Unfortunately I cant use the same software, as it only runs on Windows

Is there any possibility that slicer could enable this function, Thanks