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Motion Path not smooth on short animation

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Sam Peckham
Motion Path not smooth on short animation
on May 13, 2009 at 11:04:17 am

Hi,

I'm using a bezier curve as a motion path and adding a particle emitter to it, so it looks like a pen ringing around a subject.

This looks great over a long animation time, but if I shorten the 'motion path' behavior to around a second (the desired length), the path suddenly becomes very angular. I only have 4 points on the path and I'm using the bezier handles to smooth a circle out. However the animated path seems to break down into 20 or so angular points.

It seems to add more and more points to the curve until I hit a length of 60 frames (2s) at which point it goes back to a perfect curve. I've tried increasing the birth rate massively, played with the particle shape (it's using the marker image from shape style). The particle life is long enough too.

Is this just a limitation of Motion or perhaps my graphics card or Mac power? Or have I missed a step. Resolution is on full too, render quality is Normal.

Interestingly, on the bezier points, the 'very smooth' option is greyed out.

Any thoughts,

Many thanks
Sam




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Jim Johnson
Re: Motion Path not smooth on short animation
on May 13, 2009 at 9:50:17 pm

Howdy,

If you're working on a 30fps project, I would hazard that there are 30 segments in that curve. What you're likely running into isn't a limitation of Motion, per se, but limitation of animation. Let's assume a 30fps project. The behavior is set to move the emitter along the curve in 30 frames. The way Motion (or any application or even paper-and-pencil animator) does this is find 30 points along the path, one for each frame. On each frame, the emitter will be at one of those points. With a long enough curve or short enough span of time, those points will be spread out (spatially) and give only a jagged approximation of the curve.

If you were animating the position of a visible object, like some text or an image, persistence of vision would smooth out the movement in the viewer's brain. But because you're using an emitter to lay down a "track", the approximated (chunky) path is shown.

As you've noticed, you can work around this by increasing the duration of the behavior or by shortening the path. Depending on the effect you're going for, you might want to see if you can use the path as a paint stroke (i.e. change the shape's type to Paint) and use the Write On behavior to animate its appearance/disappearance. Paint strokes can be stroked with images, so you could use the same source image as you are using with the emitter, possibly achieving the same result.

A final, kludgey—but maybe effective—route is to lengthen the behavior till the emitter comes out smooth, render it out by itself, reimport it as footage, and then retime it down to the desired length. This works, but it's change-unfriendly, as you'd have to re-render the emitter for anything but a simple color-correction change.



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Sam Peckham
Re: Motion Path not smooth on short animation
on Jun 15, 2009 at 1:02:58 pm

Jim,
Just wanted to say many thanks for the great reply. It explained exactly what the problem was, which i feel I should have worked out if only I was paying more attention (I was focussed on it being a Motion problem, not an animation principle!). Anyway, got the project done and extended the animation time in the end.

Many Thanks

Sam


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Brandt Krueger
Re: Motion Path not smooth on short animation
on Jun 25, 2010 at 5:02:23 pm

Jim,

This was a perfect explanation of this situation. I've run into the same thing, and like Sam it hadn't occurred to me that it was a timing issue. Your solution isn't kludgey at all. I doubled the length of my animation and the path smoothed out. Then, when I brought it into FCP I doubled the speed and it looked great!

Thanks,
Brandt


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