Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!usc!apple!well!nagle
From: nagle@well.sf.ca.us (John Nagle)
Newsgroups: comp.graphics
Subject: Re: Luxo lamp jumps hurdles
Message-ID: <21304@well.sf.ca.us>
Date: 23 Oct 90 06:19:34 GMT
References: <41853@eerie.acsu.Buffalo.EDU>
Lines: 29

v134kkut@ubvmsb.cc.buffalo.edu (David W Tinklepaugh) writes:

>I read this fascinating article once, but can't remember where.  
>These guys were animating a Luxo lamp on a computer.  They gave each joint
>a maximum strength; told it it had to jump over an invisible 
>hurdle placed a certain height a certain distance in front of it.  ...

     The article is "Spacetime Constraints", by Andrew Witkin and Michael
Kass, and it appeared in ACM Trans. on Computer Graphics, Vol 22, #4, 
August 1988.  

>What is this called?  parameterization?  goal orientated programing? 
>object/environment interaction?  

     It's called nonlinear optimization.  This is a very powerful
technique, but it requires extensive CPU resources.  Kass's first
implementation took 20 minutes on a Symbolics 3600 to compute a simple
jump.  A later implementation, which used Mathematica to differentiate
and simplify the functions involved so that C code could be generated and
linked into the optimizer, required only 20 seconds on a 25 MIPS machine.

     I encourage people to read up on this technique and pick up from
where these people left off.  The work was going well, but Schlumberger
decided to get out of the AI business and closed its Palo Alto lab,
where this work was done.  Witkin is now at CMU, and Kass is at Apple.

     If someone plans serious work in this area, please let me know.

					John Nagle