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# Point on the surface of a sphere (rotating)

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 Point on the surface of a sphere (rotating) on Jun 21, 2011 at 4:46:13 pm

Greetings! I have a need for a null to move along the surface of a sphere, randomly (or adjustable). I am wondering what the expression would be for this, so I can adjust the radius of the sphere? I know Dan Ebberts has a great expression here:
http://www.motionscript.com/mastering-expressions/random-sphere.html

That would seem to work if I could just use one point, then "wiggle" it around, possibly. But I don't understand the expression enough to know how to adjust the speed that the null moves around, and how I can make it move in more of a gyroscope kind of motion, if I want it to. Any thoughts?

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 Re: Point on the surface of a sphere (rotating)on Jun 21, 2011 at 5:04:48 pm

How about just putting a null at the center of the sphere, parenting your layer to that, then rotate the null (or wiggle its rotation properties) however you want?

Dan

 Re: Point on the surface of a sphere (rotating)on Jun 21, 2011 at 5:10:28 pm

That's EXACTLY what I've been playing with now. I had thought I wouldn't be able to get the global position value of the null if I did that, but thanks to another of your expressions:

L = thisComp.layer("Null 1");
L.toWorld(L.anchorPoint)

...I was able to! Now I'm just creating a set of sliders so I can adjust the value of the radius and various properties.

I thought there might be a way to just do all of this without parenting, only using expressions. But parenting a null to a "Center" null with rotation definitely seems to give me the control I wanted. It doesn't quite move in a gyroscope-ish way, but that might be a matter of me tweaking the values more. Thank you for your help!

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