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Eccentric (elliptical orbit around null object)

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Rahman Henderson
Eccentric (elliptical orbit around null object)
on Feb 21, 2019 at 7:04:10 am
Last Edited By Rahman Henderson on Feb 21, 2019 at 7:15:39 am

I have made a planetary orbit animation such as in this video:



, except mine is top-down view. It is intended to show the orbits of moons in correct time and approximate 2D position.

Essentially two circles, viewed from the top, one paired to a null object that shares the anchor point with the other circle, orbiting using Z rotation.

I need to change the orbit from circular to elliptical, with an eccentricity of 0.75

How would I do this?

One post on here recommended I do this: https://forums.creativecow.net/archivethread/2/482236#482525

But I'm not sure where to enter that code, or if that will even work. I think I enter the position expression by alt-clicking something, but I dont know where it goes or how to format it.

I am very new to AE, this is my first project although I have been using PS for a very long time.

Any help greatly appreciated!


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Walter Soyka
Re: Eccentric (elliptical orbit around null object)
on Feb 21, 2019 at 10:39:30 am

That expression should work for you. You'd have to calculate the width and height of the ellipse you wish in pixels and set them in the expression (they are currently 600px and 400px, respectively).

Alt+click the Position stopwatch and paste it in.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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Rahman Henderson
Re: Eccentric (elliptical orbit around null object)
on Feb 23, 2019 at 4:39:52 am

I got it working. I now realize that the final line is the array that is the position expression. Everything else is just inconsequentially named variables used to populate the final array.

What if I wanted to display the position of the object on screen? Is there a way to link some text on the screen to one of those variables in the position expression?

Precisely, I want to display the distance of the moon from the planet it is orbiting, as well as the time (taking the values and multiplying them by whatever value is necessary to get them from pixels to astronomical units)


Thank you very much!


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