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How to find the true scale of a 3d object.

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Richard GarabedainHow to find the true scale of a 3d object.
by on Dec 12, 2014 at 11:05:46 pm

Say i have a layer at 50% scale. I move it back 1000. now what is its true scale value? Of course i will usually just eyeball it. If its too pixelated i undo or change out the shot. Really im just curios.


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Walter SoykaRe: How to find the true scale of a 3d object.
by on Dec 15, 2014 at 3:48:57 pm

scale = Focal Length / (Focal Length + z depth into screen)

In Ae, the 2D scale equivalent of a reference 3D layer, roughly expressed for a default camera:

l = thisComp.layer("3D Layer");
focalLength = thisComp.activeCamera.zoom;

s = focalLength / (focalLength + l.position[2]);
[s,s] * l.scale[0];


This covers the simplest case only. It doesn't deal with non-centered anchor points or parenting, nor does it get into the vector math for calculating the distance of a layer down the camera's Z-axis. We can re-visit these topics, too, if you need to.

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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