• Adobe After Effects Expressions

  IK update (keeping the feet level)

  Posted by Dan Ebberts on September 26, 2007 at 1:45 am

  Earlier this month there was a question about how to keep the feet level when using the revised IK expressions. I’ve been scratching my head for weeks over this. It seems like it should be really simple to just calculate the foot’s world orientation and rotate that amount in the opposite direction. But in trying to make that work, I’ve seen some unbelievably bizzare results from the expressions. I’ve come to the conclusion that when you create a complex chain of expressions like these, you have to watch out not to create an expression “loop” where, essentially, two expressions reference each other.

  So, (if anybody’s still interested) I think I finally cracked it. What seems to work is to apply a Transform effect to the foot. For the Transform’s anchor point and position you need to apply this simple expression:

  anchorPoint

  Then apply this expression to the Transform’s rotation property:

  v = toWorldVec([1,0,0]);
  -radiansToDegrees(Math.atan2(v[1],v[0]))

  Dan

  John Hammond replied 17 years, 3 months ago 3 Members · 2 Replies
• 2 Replies

• 

  Mike Clasby

  September 26, 2007 at 5:24 am

  Sounds exciting, will test it tomorrow.
• 

  John Hammond

  February 9, 2009 at 11:51 am

  I’ve just tested this out in AE,
  Working great for me, I can see many cases where this will be useful.

  Could it be modded to make the ‘foot’ point at a target point, rather than ‘downwards’ ? for example a robot arm with a lazer on the end that’s ‘locked on’ to a moving point target..

  Just a thought – expressions are still new to me.

  Thanks for the knowledge.
  John

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