Hi everyone, recently I've been working on interpolating two orientation values smoothly in after effects expression. And I want to use only expression, no keyframes, so it can be dynamic.
Here is my scenario. I have two cameras that are in different position and rotation status and I want to morph between them on the third camera.
![1.png]()
The position and point of interest property, I can handle them with my expression. But the interpolating process of orientation property is going crazy.
![Probmatic Orientation.gif]()
My expression used on orientation property is as below:
var C1 = thisComp.layer("Camera 1");
var C2 = thisComp.layer("Camera 2");
var C1Orient = getWorldOrient(C1);
var C2Orient = getWorldOrient(C2);
linear(time,0,10,C1Orient,C2Orient);
function getWorldOrient(L){
var u = fromWorldVec(L.toWorldVec([1,0,0]));
var v = fromWorldVec(L.toWorldVec([0,1,0]));
var w = normalize(fromWorldVec(L.toWorldVec([0,0,1])));
var sinb = clamp(w[0],-1,1);
var b = Math.asin(sinb);
var cosb = Math.cos(b);
if (Math.abs(cosb) > .0005){ var c = -Math.atan2(v[0],u[0]); var a = -Math.atan2(w[1],w[2]);
}else{
var a = (sinb < 0 ? -1 : 1)*Math.atan2(u[1],v[1]); var c = 0;
}
return [radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)];
}
Basically, I get the world Orientation of those two cameras, then linearly interpolate between them. But it doesn't work well.
Then I got another expression as between
var C1 = thisComp.layer("Camera 1");
var C2 = thisComp.layer("Camera 2");
var u1 = fromWorldVec(C1.toWorldVec([1,0,0]));
var u2 = fromWorldVec(C2.toWorldVec([1,0,0]));
var v1 = fromWorldVec(C1.toWorldVec([0,1,0]));
var v2 = fromWorldVec(C2.toWorldVec([0,1,0]));
var w1 = fromWorldVec(C1.toWorldVec([0,0,1]));
var w2 = fromWorldVec(C2.toWorldVec([0,0,1]));
var u = linear(time,0,10,u1,u2);
var v = linear(time,0,10,v1,v2);
var w = normalize(linear(time,0,10,w1,w2));
var sinb = clamp(w[0],-1,1);
var b = Math.asin(sinb);
var cosb = Math.cos(b);
if (Math.abs(cosb) > .0005){ var c = -Math.atan2(v[0],u[0]); var a = -Math.atan2(w[1],w[2]);
}else{ var a = (sinb < 0 ? -1 : 1)*Math.atan2(u[1],v[1]); var c = 0;
}
[radiansToDegrees(a),radiansToDegrees(b),radiansToDegrees(c)];
In some cases it works, but in some it doesn't. Such as below:
![problem2.gif]()
Here is the project file if you want to take a look at:
https://www.sendspace.com/file/jv05o4
So I am wondering how I can interpolate between them. I heard about quaternion. But It seems that quaternion is not built in after effects expression. And it is way beyond my ability.
Anyone's help will be appreciated!
Thanks,
Aaron
