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Auto Orient Y only – remain parallel horizontally
Hey guys,
I’m a longterm user of Dan Ebberts’ Auto Orient Y Only expression. I have a requirement that’s a little bit more advanced and I can’t quite work out how to do it.
The problem is, when auto oriented objects move away from camera centre, there is a twisting occurring. Usually I’d use another Ebberts’ expression to deal with this (‘Orient to Camera Plane’) – but I can’t work out how to combine the approaches.
Basically I want the auto orient to always ensure that horizontal lines are parallel to the camera plane.
If this isn’t super clear, I made a short video (<2min) explaining the issue.
If anyone could help out I’d be extremely grateful,
Thanks, Nathan
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4 Replies
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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 -
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
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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.
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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.
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