Author Topic: Rotation about an external point after translation  (Read 1746 times)

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Offline harisali110

Rotation about an external point after translation
« on: September 11, 2017, 04:28:52 am »
Hi,

I am trying to animate a situation where object-1 moves a certain distance (say 500mm) towards object-2 and then rotates about object-2. There is still some distance between object-1 and object-2 (say 250mm) at the start of rotation.

The problem I am facing is that Keyshot is calculating the terminal radius of the rotation as if it is unaffected by the translation of object-1 (radius of rotation = 750mm). The rotation starts off fine from the correct location (radius of rotation = 250mm) but ends up taking an elliptical path to terminate with radius of rotation 750mm in this case.

If I turn off the translation, rotation is fine with the radius at 750mm. Thanks in advance for the help. I am using Keyshot 6 btw.

Offline Esben Oxholm

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Re: Rotation about an external point after translation
« Reply #1 on: September 11, 2017, 07:23:21 am »
Hi harisali.

This is not an optimal solution as it is quite limited, but if you start by positioning object1 250mm away from obj2 and do an 'setup' animation where obj1 moves 500mm away from obj2, then you can do what you want. Animate obj1 500mm towards obj2 and then do the rotation.

See the described setup here: https://we.tl/oUCXx46d4K

Offline mattjgerard

Re: Rotation about an external point after translation
« Reply #2 on: September 11, 2017, 07:57:54 am »
Hi harisali.

This is not an optimal solution as it is quite limited, but if you start by positioning object1 250mm away from obj2 and do an 'setup' animation where obj1 moves 500mm away from obj2, then you can do what you want. Animate obj1 500mm towards obj2 and then do the rotation.

See the described setup here: https://we.tl/oUCXx46d4K

This is a very common technique in animation. I learned to "animate backward" a long time ago, and it can really help solve some tricky problems. I know KS gets a little funky with translating corrdinates inside of groups, and deep heirarchies, I'm researching an issue now with support. The good thing is that they are very responsive to finding and fixing bugs like this.

Anyway, this is a good "workaround", no, its not the way it SHOULD be, but sometimes we just need to get it to work and move on :)

Offline Esben Oxholm

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Re: Rotation about an external point after translation
« Reply #3 on: September 11, 2017, 10:14:40 am »
Very interesting. Didn't know it was a common technique, but thinking about it I actually do it quite often. Starting with the end positions and then animate 'backwards'.

Offline mattjgerard

Re: Rotation about an external point after translation
« Reply #4 on: September 11, 2017, 11:11:35 am »
Yep, most of the time you know where you want the "thing" to end up, but how it gets there is where the experimentation comes in. Very common in motion graphics, logo animations, title sequences, etc. I spent 15 years doing that sort of thing. Now I'm here :)