help with cameras

I've implemented a differential drive mobile robot with a pan/tilt stereo
head in breve/steve.  However, I can't quite get the cameras to work
right.  Part of the multibody that is the robot are two links that I
call leftEye and rightEye.  They're attached via fixed joints to
links that pan and tilt.  Associated with each "eye" is a camera that
should always look in the direction the eye link is facing.

Below is the code I currently have in the iterate method for the pan/tilt
head that aims the left camera.  It gives results that are close to what I
want, but they're not quite right.

      leftCamera look at
      ((leftEye get-location) + (leftEye transform world-vector (0, 0, 1)))
      from -(leftEye transform world-vector (0, 0, 1)).

I think the camera starts out pointing in the (0, 0, 1) direction.  I'm
sure the hard-wired (0, 0, 1) needs to be replaced with a vector obtained
dynamically at the start of the simulation that's normal to the "front"
surface of the leftEye link.

Does anyone out there know the right way to keep a camera pointed in a
direction normal to a given surface of a link?

  - tim


---------------------------------------
Tim Oates, Assistant Professor
Department of CS and EE
University of Maryland Baltimore County
(410) 455-3082
http://www.cs.umbc.edu/~oates


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