I have a simple SOP network that has a circle, then a transform and for the end a trail SOP, the transform is animated in the tx channel, it has two keyframes, one in the beggining and the other in the end frame. The animation curve is linear, so i supose that the velocity is constant.
But in the trail SOP i use Compiute velocity and the rest of the parameters in their default values, if a use a spreadshet to see the velocity atribute along the animation i can see that for the first 76 frames the velocity is constant, 1.75, but from this frame the velocity isn't constant, if the animation curve that govern the animated chnnel is linear the velocity must be constant, or no??
Please some clues
Thanks

lisux
I have a simple SOP network that has a circle, then a transform and for the end a trail SOP, the transform is animated in the tx channel, it has two keyframes, one in the beggining and the other in the end frame. The animation curve is linear, so i supose that the velocity is constant.
But in the trail SOP i use Compiute velocity and the rest of the parameters in their default values, if a use a spreadshet to see the velocity atribute along the animation i can see that for the first 76 frames the velocity is constant, 1.75, but from this frame the velocity isn't constant, if the animation curve that govern the animated chnnel is linear the velocity must be constant, or no??
Please some clues
Thanks

The trail SOP's compute-velocity works by cooking the input, then cooking the input at $F-1, and setting v to the difference

(T-T)*$FPS.

As far as constant curve generating constant velocity, it should be true everywhere except at keyframes, where you could introduce a change in the slope. Your first frame's velocity will probably be incorrect.

– Antoine

Antoine Durr
Your first frame's velocity will probably be incorrect.

I often insert a Point SOP in the SOP chain to set that initial velocity (before the Trail SOP).


–Mark

Thanks Antoine, the Trail SOP works like i expects, i make a mistake when i supose that a linear segment is equal to constant velocity, sorry about my maths mistake, this is only true in some cases, when the relation between frames and space is always the same.