linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

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cameralibre
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linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby cameralibre » Fri May 26, 2017 10:44 am

Ever since I began working with Synfig, I have been confused by waypoint interpolation, and I often find that settings which I think will give me a smooth arc instead cause a slow-fast-slow-fast movement, or my animations follow unexpected curves.
Maybe somebody can help me wrap my head around this using an example project (see attached).
smooth-motion.sifz
(3.22 KiB) Downloaded 54 times


Note: I know that this can be achieved by following a spline, but this is to help me understand movement with waypoint interpolation, so that is how I would like to do it. I have read the documentation on interpolation and I am still very confused.

Essentially what I would like is linear speed but a curved shape, between waypoint 1 and waypoint 4, following the blue line. I have tried editing the TCB settings and improved on the original default settings, but both attempts are still way off.
Often when I try to do this it ends up creating an obvious 'corner' at waypoints 2 and 3. I don't want the circle to slow down at all as it passes them, I essentially want waypoints 2 & 3 to be invisible to the viewer. It seems like reducing the Tension setting improves this aspect, but I can't get it to a constant linear speed.

Image
Image

Do I need to include extra waypoints either side of these (i.e. waypoint 0 and waypoint 5) in order to achieve the curve that I want?
Any other suggestions for more reliable/more accurate use of waypoint interpolation?

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Svarov
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Re: linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby Svarov » Wed May 31, 2017 2:18 am

TCB interpolation is a mystery to me. I tried to use it sometimes but its overshooting can't be easily controlled. I always thought TCB can be represented as a curve similar to two-vertex outline, so if you hit 'Edit TCB' you'd see a standard handles of a curve, but I can be totally mistaken.

Anyway, I am interested in this topic too. It would be nice to see some practical examples in which TCB interpolation is useful with a detailed explanation.

Now working on: Wolf's head turn (test 7)

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cameralibre
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Re: linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby cameralibre » Wed May 31, 2017 1:35 pm

Yeah, I find it really frustrating too. It seems like such a basic element of animation, yet in Synfig, I am really stuck on it.

Do you have any other non-TCB tricks to get smooth arc movement as I described (other than following a spline)?

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Svarov
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Re: linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby Svarov » Thu Jun 01, 2017 1:58 am


Now working on: Wolf's head turn (test 7)

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cameralibre
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Re: linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby cameralibre » Thu Jun 01, 2017 7:13 pm

Thanks for your thoughts on this, hmm, yeah, it's a bit of a mess alright! I completely agree about the need for visual handles to set interpolation rather than trying to get TCB to work by throwing numbers at it :)

I just realized that this post should be in the forum category, not 'general discussion - but I can't see a way to move it.
If an admin sees this, please feel free to move it!
Thanks

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BobSynfig
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Re: linear speed, but curved motion: difficulty adjusting TCB interpolation to follow an arc

Postby BobSynfig » Thu Jun 01, 2017 11:23 pm

Always check first! - Use last builds only: Stable 1.2.1 /
- - - Google Translate may help


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