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# Question about fixing objects together

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 Question about fixing objects together on Sep 11, 2011 at 12:09:46 pm

Hello

Say I have a circle on the end of a long rectangle. I attach the circle to the end by Parenting it. I now have a circle always attached.

I have two queries. one, why doesn't the circle now have any positions of its own?
and two, because the circle has no position coordinates, how would I attach CC particle Systems II onto it?

I'm hoping to create a kind of, firework-spinner but my idea of how it would work ran into problems when objects stop using the coordinates when set as the child position.

Thanks.

 Re: Question about fixing objects togetheron Sep 11, 2011 at 2:52:50 pm

It is best to apply Particle World to a Comp sized Solid layer.

In your case the issue is how Particle World calculates its coordinates relative to the Composition. You can use an expression to tie the XY and Z position of the particle producer to another layer, generally a Null object.

See this example: 2926_particleworldwithnull.aep.zip

 Re: Question about fixing objects togetheron Sep 11, 2011 at 3:09:37 pm

Thanks. checking this out now.

I guess I should now be able to create the spinner I had, where the particle system is attached to a long rectangle edge and the rectangle spins in the center with the particles emitting around 360.

Thanks.

 Re: Question about fixing objects togetheron Sep 11, 2011 at 5:24:55 pm

The circle still has position coordinates after it becomes a child of the rectangle. The difference you are noticing is that the circle's position property is now relative to the coordinate system of the rectangle. This is one of the things that makes parenting so powerful, it allows you to create a chain of animations that occur relative to the parent's (or parent's parent's) coordinates.

You can still access the circle's "real" world position but it requires an expression:

``` l = thisComp.layer("Circle"); p = l.toWorld(l.anchorPoint); ```

The 'p' variable will contain the world coordinates of the circle's anchor point. You can apply this to the emitter property of a particle system.

Darby Edelen