Full auto-orient via expression

Question

Hi!I'd like a 3D Null to get the orientation of 3D a layer. (without parenting, it would be too easy )I've tried a lot of solutions, through orientation, rotations, both combined... some results are close, but never perfect.If I'm right, orientation is computed before rotations...I think the simplest way would be with auto-orientation, or the lookAt() expression on orientation, wich gives me correct X and Y orientations, and then get an expression on zRotation to get a "full" orientation.But what would it be? How can I get the Z orientation in layer space?Any idea will be appreciated!François

Dan Ebberts · Accepted Answer

Try this oreientation expression:L = thisComp.layer("other layer");u = fromWorldVec(L.toWorldVec([1,0,0]));v = fromWorldVec(L.toWorldVec([0,1,0]));w = normalize(fromWorldVec(L.toWorldVec([0,0,1])));sinb = clamp(w[0],-1,1);b = Math.asin(sinb);cosb = Math.cos(b);if (Math.abs(cosb) > .0005){ c = -Math.atan2(v[0],u[0]); a = -Math.atan2(w[1],w[2]);}else{ a = (sinb < 0 ? -1 : 1)*Math.atan2(u[1],v[1]); c = 0;}[radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)]Dan

synthetick · Answer

This thread has helped me a lot but I'm stuck on something. I'm trying to set up expressions for an animation of an office chair. I have a 3D null called "null - direction" which controls the path of the chair, and it is set to auto-orient along the path. But I wanted the wheels to have a slight delay so that when the chair turns a corner the wheels take a little bit of extra time to rotate into that orientation.

In order to do this I made a null called "null - getOrientation" and I used the expressions in this thread to get the orientation of the chair, and then I used another null called "null - delay" to delay the orientation by half a second. The orientation of the wheels is pick-whipped to the orientation of "null - delay"

It all seems to work ok at the first corner but when we get to the second corner the chair is turning clockwise but "null - getOrientation" and "null - delay" start turning anticlockwise and we end up with wheels not oriented to the path. I'm attaching a video which I hope shows what I mean. On further investigation it seems to be occurring when the value of sinb reaches the top or bottom of the sine wave curve ie. at 1 or -1.

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