Auto Orient Y only – remain parallel horizontally

[Dan Ebberts]

That’s a tricky one. This seems to work until the angles get too extreme (but there’s probably a better way):

v = fromComp([1,0,0]);
v1 = normalize([v[0],0,v[2]]);
v2 = [1,0,0];
radiansToDegrees(Math.acos(dot(v1,v2))) - 90

[Nathan Clark]

Hi Dan, thanks so much for giving this a bit of thought. Sadly this new expression actually seems to make things worse 😬. I put together another video demonstration presenting a side-by-side with the original (auto orient Y) and the new expression – showing how it’s basically identical from one aspect, then gets progressively funkier as we orbit the camera around the 3d solid. Just in case it’s helpful, I’ll attach the project file. But also, if there’s no simple solution please don’t let this trouble you any further, I can always make a compromise and abandon this part of my treatment if need be. Thanks Nathan

https://youtu.be/otEnb_C5eH4

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Orientation-demo.aep 202 KB After Effects Project Files - Click to view

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[Dan Ebberts]

I think part of the problem is that it’s not hard to conjure up a situation where just rotating on the y axis can’t make the top edge appear horizontal in the camera view, so I think it may be a problem with no solution in some situations.

[Nathan Clark]

Ah okay, so this I must counter! I believe that in every situation rotating the Y can make the top and bottom edges both appear perfectly horizontal, simultaneously. I intuitively know this thanks to a past-Nathan who was into doing perspective drawing. To prove this, another short video presentation. Again, no offence will be taken should you lose interest here, I just didn’t want to write it off as impossible for the above reason.

https://youtu.be/3UWlx0KsKlU

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