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sub-frame motion path accuracy

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Nick Hillsub-frame motion path accuracy
by on Jun 7, 2012 at 1:13:10 pm

this should be really simple, but...

I've sketched a path with Motion Sketch, applied that to a null, then linked the null's position to the position of an emitter in Particular. There's one keyframe every frame, most of the time anyway. The particles are set not to move when emitted, so effectively you get the null's motion path traced out. However there are visible corners on it - AE seems to be just joining the keyframes with straight lines rather than smoothing these out. I suppose I could just stretch the keyframes out and then speed the footage up, but is there any other way of changing the interpolation?

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Roland R. KahlenbergRe: sub-frame motion path accuracy
by on Jun 7, 2012 at 2:00:05 pm

The Smoother KF Assistant often comes in handy after a Motion Sketch routine. Ensure that you select the KFs that you want to smooth. This will enable the Smoother's UI. Set Tolerance to a high value for smoother results. The number of KFs will be reduced and the path will be smoother as a result of applying Smoother.


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Darby EdelenRe: sub-frame motion path accuracy
by on Jun 7, 2012 at 3:01:13 pm

There's also a fairly straightforward smooth() expression function. If you apply it exactly as I've written it above then you should get a smoother result out of the box.

If you need to adjust the smoothing then there are a couple of simple parameters you can change. The first is the 'width' of the smoothing which defines the amount of time around the current frame to use for the smooth, the default is 0.2 seconds. The second is the number of samples to take across this width/duration, you should usually use an odd number here so that a sample falls on the current frame, the default is 5 samples.

So, if you want less stair-stepping in the keyframe interpolation you can increase the samples, and if you want the curve to match the original path more closely you can decrease the width:

smooth(0.1, 17);

I'd recommend changing the values while you look at the temporal graph of the expression.

Darby Edelen

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Darby EdelenRe: sub-frame motion path accuracy
by on Jun 7, 2012 at 3:04:59 pm

Also, the emitter position in Particular has a few different options under Position Subframe. I'd recommend 10x Linear if you're seeing ugly linear bits in your emitter path. This has the effect of smoothing the emitter's motion path and may do the job without any additional smoothing via the smoother or an expression.

Darby Edelen

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Nick HillRe: sub-frame motion path accuracy
by on Jun 7, 2012 at 3:16:10 pm

Thanks all. I wasn't aware of the position subframe options (hidden in plain view??) but that's actually pretty much exactly what I was thinking of.



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