Design Realization lecture 2

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Design Realization lecture 2

• John Canny
• 8/28/03

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Last Time

• Design Realization about the creation of smart
  and often networked artifacts.
• Goal is fluency in several design media, (3d
  shape, animation, mechatronics, optics), and
  interdisciplinary collaboration skills.
• Class consists of short exercises, contributions
  to the knowledge repository, and a longer project.

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Updates

• Class home page iswww.cs.berkeley.edu/jfc/DR/F03
  
• Class swiki (password needed) is up
  atkettle.cs.berkeley.edu/DesignRealization2
  please submit summaries there by next Tues.
• Maya will be available on some machines in HMMB
  but also on CD for personal class use.
• First Maya assignment will go out next Tuesday
  due in two weeks.

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Section 1 3D Shape

• We start by listing some qualities of 3D shape
  (exercise)

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Section 1 3D Shape

• We start by listing some qualities of 3D shape
  (exercise)
• Try enumerating good shapes (natural and
  artificial)

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3D Shape Creation

• Since most people lack 3D input devices, Its
  usually best to work mostly with 2D shapes
  (curves) and lift them to 3D.
• The 2D shape can remain an efficient way to edit
  the 3D shape.
• c.f. McCulloughs notion of grain how?

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Curve Creation

• Three ways in Maya
• Freehand drawing
• Setting control points (not on the curve)
• Setting curve points
• All 3 actually produce NURB curves (Non-Uniform
  Rational B-splines)

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Curves

• Curves have tangents at every point, that define
  the curves direction.
• A tangent is the straight line which is the limit
  of curves formed by zooming in to the point.
• Polygonal lines have abrupt changes in tangent at
  vertices. Spline curves (e.g. NURBS) allow smooth
  tangents from one curve segment to the next
  (sketch).

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Curves

• Most 3D systems use parametric curves.
• Parametric curves have a single parameter that
  varies along the curve, usually from 0 to 1.
• Parameters make it easy to compute tangent
  curves, and to walk along the curve (e.g. for
  displaying it).

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3D geometry

• 3D worlds are defined by 3 (cartesian)
  coordinates X, Y, and Z.
• For historical reasons, in most 3D systems, Y is
  up and Z is toward the viewer.
• These three directions also define three standard
  views of objects. In addition, there is usually a
  perspective or orthographic view from a general
  camera position.

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3D geometry

• A 3D shape has six degrees of movement freedom
• 3 degrees of translation along X, Y, Z
• 3 degrees of rotation about X, Y, Z

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3D puzzle

• In Maya, the six degrees of freedom are mapped to
  mouse movement (two DOF), with one of 3 mouse
  buttons down (a total of six).
• BUT
• Mouse middle allows translation in X, Y.
• Mouse right allows translation only in Z.
• Mouse left allows all three rotational DOF.
• In other words, one mouse DOF is wasted, and we
  get all 6 motion DOFs from 5 mouse DOFs. How??

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Resources to answer this question

• Good books Hearn and Baker Computer Graphics
  (C version), Prentice-Hall
• Links
• JFCs notes JFC/past courses/CS184
• Laura Downs notes on quaternionswww.cs.berkeley.
  edu/laura/cs184/quat/quaternion.html
• Discussion relate this to McCulloughs notion of
  direct vs. indirect manipulation.

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3D surfaces

• NURB surfaces are built from NURB curves, and
  smoothly skin between them.
• Surfaces are also parametric, with two parameters
  this time (u, and v), typically between 0 and 1.
• Each surface point has two tangents (one each
  along u and v directions), and a normal which is
  off the surface.

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Continuity and degree

• The default NURBs in Maya have (algebraic) degree
  3. A curve has degrees of freedom as well
  (sketch).
• The higher the algebraic degree, the more degrees
  of freedom the curve has.
• Higher degrees of freedom allow higher degrees of
  smoothness (or continuity) between curve
  segments.

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Continuity and appearance

• High continuity is important for appearance of
  smooth, glossy surfaces. Automotive models may
  need 4th order or higher continuity.
• Other properties, especially curvature, may be
  limited by the fabrication process.

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Resources again

• Good books on graphics Hearn and Baker
  Computer Graphics (C version), Prentice-Hall
• Links
• JFCs notes JFC/past courses/CS184
• The Maya 4.5 Bible

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Wrap-up

• Finish the Itten and McCullough readings.
• Write short summaries (lt 1 page), and post to
  Swiki by next Tuesday. Wait til tomorrow for
  submission page.
• Maya CDs should be available on Tuesday next
  week, when the assignment will go out.