Design Realization lecture 7

1
Design Realization lecture 7

• John Canny
• 9/15/03

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Preamble

• Blog for Maya is up now, but you need to be added
  as an author. Mail one of the current authors.
• We will finish project review today.

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Last Time

• Materials and textures.
• Displacement and bump mapping.
• Texture coordinates.
• Qualities of movement.
• Keyframing
• Specify sample poses and transitions.
• Edit trajectories like curves.
• Elements of a movement.
• Anticipation, Action, Recovery.

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Kinematics

• Kinematics (from kinema/cinema to move).
• Kinematics typically involves chains of joints,
  to represent movement of living things.
• Transformations are applied from the beginning to
  the end of a kinematic chain
• E.g. from shoulder to fingers

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Kinematics

• If p is a point and T is a transformation matrix,
  then Tp is the new position of p.
• If joints are numbered from 1,,n, then the
  position of a point on the last link is
• T1 T2 (T3 (Tn p))
• In other words, the finger is moved by the
  shoulder, elbow and wrist joints.

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Local joint coordinates

• Because transformation matrices change
  coordinates of points, the position of joint axes
  is not unique.
• The standard method is to use a local coordinate
  system for each link.
• Z axis is aligned along the joint.
• X axis is aligned normal to both joints.
• Therefore X displacement measures link length.

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Local joint coordinates

• Maya places the local coordinate transforms
  information in a joint attribute.
• You always see the joint transform as a zero
  rotation, with an X displacement to the next
  joint (the link length).

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Inverse Kinematics

• Whenever we reach for something or take a step,
  we have to solve for many joint angles this is
  inverse kinematics.
• Maya provides several kinds of solver that allow
  you to control hands, feet etc. directly.
• They create virtual objects (handles) that can be
  moved and keyed in the usual way.

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Todo

• Chair designs due on Swiki by Thursday.
• Make sure you get added to the blog editors list.
  
• Extra material shaders and MayaBible
• Just copy onto your disk