• Adobe After Effects Expressions

  How to call for a value before expression?

  Posted by Simon Björk on December 30, 2010 at 10:05 am

  I’m trying to reposition a camera to start at z-position 0.

  For example, I have a camera that has a position of [960,549,-8000].

  I want to move the z-position to 0, so I add the following expression “position + [0,0,transform.position[2]*-1]”. I can’t call the actual value, becuse this expression will be a part of an autumated process and the camera position will be different for different projects. All this works perfectly, but I have some other obects that I want to move the same ammount. For example, I have a null at z-position 10, and would like to move that the same ammount as the camera (which would give me a value of 8010 in this example.

  I tried with the following expression to the null: “position + [0,0,thisComp.layer(“Camera 1″).transform.position[2]]”, but that doesn’t work since the cameras z-position has been moved to 0 already. So I must call the cameras original z-position somehow. Is this possible?

  Dan Ebberts replied 15 years, 7 months ago 3 Members · 5 Replies
• 5 Replies

• 

  Chris Wright

  December 30, 2010 at 6:28 pm

  put this in null position.

  r=thisComp.layer(“Camera 1”).transform.position.valueAtTime(effect(“Slider Control”)(“Slider”));

  value+[0,0,r[2]];

  https://technicolorsoftware.hostzi.com/
• 

  Simon Björk

  December 30, 2010 at 8:24 pm

  Thank you for your reply Chris, but nothing happens with that expression, even if I add a slider to the null. Am I supposed to change any values?
• 

  Dan Ebberts

  December 30, 2010 at 8:29 pm

  Try this little trick. Change your camera’s expression to this:

  if (time < 0)
  value
  else
  position + [0,0,transform.position[2]*-1];

  and the null’s expression to this:

  position + [0,0,thisComp.layer(“Camera 1”).transform.position.valueAtTime(-1)[2]]

  Dan
• 

  Simon Björk

  January 4, 2011 at 9:35 am

  Hi Dan, thanks for your reply.

  I don’t get your expression to work either.

  It does change the nulls position correctly if I change your “position + [0,0,thisComp.layer(“Camera 1″).transform.position.valueAtTime(-1)[2]]” to position + “[0,0,thisComp.layer(“Camera 1″).transform.position.valueAtTime(-1)[2]*-1]”.

  However, I I want to animate my camera, I can’t. If I use the z-slider, it just moves the null and snap back to position 0.

  Any ideas?
• 

  Dan Ebberts

  January 4, 2011 at 4:05 pm

  Ah, OK. I didn’t understand that you were animating the camera. Try it this way:

  camera:

  if (time < 0)
  valueAtTime(-time)
  else
  position + [0,0,transform.position[2]*-1];

  null:

  position + [0,0,thisComp.layer(“Camera 1”).transform.position.valueAtTime(-time)[2]]

  Dan

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