Calculating angle from camera to object – expression

[Dan Ebberts]

It’ll probably be some variation of something like this:

C = thisComp.layer(“Camera 1”);
v1 = normalize(position – C.position)
v2 = C.toWorldVec([0,0,1]);
radiansToDegrees(Math.acos(dot(v1,v2)))

Dan

[Colin Braley]

Dan,
I was reading through this expression trying to figure out how it works and ive got a few questions. I typed out what I think each line does but im not sure about line 3…

C = thisComp.layer(“Camera 1”);
//var C = the camera

v1 = normalize(position – C.position)
//v1 is the direction vector from the camera to the layer (it has length 1)

v2 = C.toWorldVec([0,0,1]);
//what is this line doing?

radiansToDegrees(Math.acos(dot(v1,v2)))

//so here you are finding the angle between v1 and v2 and outputting it in
//degrees because v1 dot( v1 , v2 ) = length(v1) * length(v2) * cos( theta )
//where theta is the angle between the two vectors…but since v1 and v2 are //normalized you are just using the arccos to get the angle between the two //vectors

Thanks in advance Dan.

~Colin

[Dan Ebberts]

Colin,

Your analysis is dead on.

v2 = C.toWorldVec([0,0,1]);

This just creates a unit vector in the direction of the camera’s z axis and translates it to world coordintes. Then you have the two unit vectors you need to find the angle.

Dan

[Colin Braley]

That makes sense now…thanks a lot Dan. I’m taking a class in vector geometry and 3d calc so a lot of the expressions you have up here finally make sense to me… 🙂
~Colin