retimer & time step & time scale
Hi. So i'm animating a sand impact from a foot, except i'm matching footage from a phantom filmed @ 800fps. Now i thought i'd be able to sim at 25 fps, then retime down to match the slowmo footage. However i'm getting some wierd interpolation as i guess it runs out of info to give me betweens that are smooth.  So the retimed particles look kinda unnatural. Can i get a smooth retime?

things i have tried:
*increasing the time step to 1/32. - this caused me to change force and gravity settings to acheive the same looking sim but i couldn't get it the same so i gave up.

*leaving the retimer off and trying the time scale spinner - this did nothing.

*retiming by frame not by speed - no difference.

Am i at the limitations of tyflow? It can't be max, as a quick setup with mass fx gives me the smooth retime i'm looking for. So i'm going for user error, in which case how do i get a good sim which enables a slow retime?
The retimer uses the cache, which is saved at rate of one data chunk per frame, regardless of what your time step setting is. It is also linearly interpolated between frames, instead cubicly interpolated. Eventually it would be nice to do cubic interpolation, which would create smooth/curved particle paths between frames rather than straight paths between frames, but that's extremely far down the priority list at the moment.

For retimings with particles following simple trajectories and the overall retime not going to extrmely slow speeds it's fine....but ramping down to 800fps with non-linear particle motion will indeed introduce visual artifacts.

One potential alternative is to export your particles to objects with the Export Particles operator and then scale their keyframes. Since keyframe curves are bezier curves by default you'll then get smooth trajectories. Obviously this method won't be great if you have a huge number of particles though.

You can also adjust your sim force values to replicate how things would look at 800fps, and then use the retimer to speed things up instead of slow it down....basically do an inverse retime from an 800fps look to a 24fps look, rather than 24 to 800.

The time scale spinner doing nothing is troubling...perhaps there's a bug and it's not working correctly...I've made a note to look into it.
Got it. ok thanks for the explaination.

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