• Adobe After Effects

  Calculating angle from camera to object – expression

  Posted by Joemason on November 8, 2006 at 8:16 pm

  I’ve been trying to figure out a way to calculate the angle between an 3D layer and a camera… specifically, a perpendicular line from the center of any given 3D object and a camera.

  The first idea I had was parenting a Null to the “object”, having it auto-orient to the camera, then calculating the absolute rotation of the Null. But in 3D space, this seems to be a tall order.

  Mainly this is to adapt Angle property controls based on camera/object angle.

  Anyone have any great ideas?

  Colin Braley replied 19 years, 6 months ago 3 Members · 4 Replies
• 4 Replies

• 

  Dan Ebberts

  November 8, 2006 at 9:47 pm

  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

  November 8, 2006 at 11:32 pm

  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

  November 9, 2006 at 2:00 am

  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

  November 9, 2006 at 2:17 am

  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

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