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How to make a 3D layer 2D and keep it's exact position in screen space?

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Dustin Bowser
How to make a 3D layer 2D and keep it's exact position in screen space?
on Dec 11, 2015 at 8:02:03 pm

In my comp I'm doing some complex projections and 3D layer manipulations for a cleanup.

I have a camera move that was 3D matchmoved, and some expressions were done to take certain patches from the plate, place them in 3D space at the appropriate depth while not having them move in any way in screen space, so that they are still lined up with the plate.

After the camera stops moving, there are some other things I need to do, including attaching these patches to a 2D track that I have. So what I'm trying to do is split my 3D layer, and have it hand off seamlessly intio a 2D version of itself that will be attached to my 2D track.

What would be the method, or the expression that would allow me take a 3D layer, make it 2D again WITHOUT it moving around even a pixel in screenspace. It looks the exact same, but is now a 2D layer.

Obviously there are ways of nudging things around, eyeballing it with difference mode or whatever, but that is not the solution I'm looking for. I know there is an expression or method that allows for this, I just don't recall what it is. It's been a while since I've had to do it.

Anyone know the method? Thanks!


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Walter Soyka
Re: How to make a 3D layer 2D and keep it's exact position in screen space?
on Dec 11, 2015 at 8:56:59 pm

An easy way would be to duplicate the comp, turn off or delete the layers you don't need in the copy, and use that reduced comp (just the patches plus the camera) as a 2D precomp layer in your main comp. This way, you don't have to worry about rotation or anything affecting perspective.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Dustin Bowser
Re: How to make a 3D layer 2D and keep it's exact position in screen space?
on Dec 11, 2015 at 9:01:22 pm

That's not a bad solution. Thanks for that Walter.

Out of curiosity, I'd still be interested to track down that expression, just to keep it handy in the toolbox.


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Walter Soyka
Re: How to make a 3D layer 2D and keep it's exact position in screen space?
on Dec 11, 2015 at 9:24:38 pm

[Dustin Bowser] "Out of curiosity, I'd still be interested to track down that expression, just to keep it handy in the toolbox."

The basic formula for expressing 3D perspective as scale is this:

Focal length / (Focal length + depth)

A simple expression of this idea in Ae:
s = thisComp.activeCamera.zoom/(thisComp.activeCamera.zoom + thisComp.layer("3D Layer").transform.position[2]) * 100;
[s,s]


Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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