Compute Speed of Spheres in 3D animation I have created two animations:


One where a "camera" moves towards the spheres creating an optic flow (1st GIF).The code can be found here.
One where spheres move randomly in a 3D coordinates space (2nd GIF). To do so I have computed two angles theta and phi. The code can be found here.


I need to compute the speed of each sphere frame by frame in both animations, but I have no idea of the mathematics. I would assume that the formula would be different in the two animations. I have found only the calculation of 3D velocity, and I was wondering whether I could calculate the speed as a single value?
I'd use the euclidean distance between two 3D positions. Velocity is distance over time. Time is a single frame in this case.

$$\sqrt{(x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2}$$

If you only move the camera, it is simply that frame of reference that moves, so all spheres have a relative velocity equal to the camera's velocity.