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Design Realization lecture 2

Design Realization lecture 2. John Canny 8/28/03. 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.

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Design Realization lecture 2

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  1. Design Realization lecture 2 John Canny 8/28/03

  2. 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.

  3. Updates • Class home page iswww.cs.berkeley.edu/~jfc/DR/F03 • Class swiki (password needed) is up atkettle.cs.berkeley.edu/DesignRealization2please 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.

  4. Section 1: 3D Shape • We start by listing some qualities of 3D shape (exercise):

  5. Section 1: 3D Shape • We start by listing some qualities of 3D shape (exercise): • Try enumerating “good” shapes (natural and artificial):

  6. 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. McCullough’s notion of “grain” – how?

  7. 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)

  8. Curves • Curves have tangents at every point, that define the curve’s 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).

  9. 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).

  10. 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.

  11. 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

  12. 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??

  13. Resources to answer this question • Good books: Hearn and Baker “Computer Graphics (C version), Prentice-Hall • Links: • JFC’s notes: JFC/past courses/CS184 • Laura Down’s notes on quaternionswww.cs.berkeley.edu/~laura/cs184/quat/quaternion.html • Discussion: relate this to McCullough’s notion of direct vs. indirect manipulation.

  14. 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.

  15. 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.

  16. 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.

  17. Resources again • Good books on graphics: Hearn and Baker “Computer Graphics (C version), Prentice-Hall • Links: • JFC’s notes: JFC/past courses/CS184 • The “Maya 4.5 Bible”

  18. Wrap-up • Finish the Itten and McCullough readings. • Write short summaries (< 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.

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