CS 285 Solid Modeling

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CS 285 -- Solid Modeling

• Procedural Solid Modeling or
• Algorithms and Data Structures for Procedural
  Design, Solid Modeling, and Rapid Prototyping
• Lets review the meaning of some of these terms
  ...
• Solid Modeling (Procedural )

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Modeling Taxonomy
CAD
Solid Modeling
CAGD (splines)
Procedural Modeling
When you spend more time programmingthan
adjusting numbers or handles
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What is a Solid ?

• Examples of solids and non-solids
• What are the key properties of a solid?

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What is a Solid ?

• Examples of solids and non-solids
• YES a block of steel, wood, styrofoam
• NO clouds, liquids,
• ? a flexible wire, a rubber gasket, cloth
  ...
• What are the key properties of a solid?
• Maintains shape in a predictable way
• Has a well-defined surface

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What is a Solid ? -- More Answers

• The Abstraction of a Solid
• Solids are composed of atoms
• Atoms are mostly empty space
• Smoothing and Sampling
• Use a finite-size probe to determine extent of a
  solid
• The Boundary of a Solid
• How far the above probe can go
• Level-set surface of a filtered density function
• Why are these considerations relevant ?
• We often make approximations to an ideal
  shape,e.g., use triangle mesh to represent a
  spline patch

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Modeling -- as in Describing

• Why do we create models of solids ?
• What do we want to do with these models ?

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Modeling -- What is the Purpose ?

• Why do we create models of solids ?
• For visualization, fabrication, analysis ...
• What do we want to do with these models ?
• Analyze mass, moments, strength, flexibility,
  beauty, reachability, assemblability, fluid flow
  in cavities, ...
• What types of models are we interested in ?
• True solid shapes, with orientable 2-manifold
  surfaces, mostly rigid, perhaps with predictable
  deformability
• and assemblies of such objects.
• What is outside scope of CS 285 Sp.2006 ?
• Collections of polygons that look like a
  forest, water, clouds, fire, rainbow (--gt
  rendering class)

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Modeling -- as in Designing

• Where do such models come from ?
• Some model capture process
• e.g., 3D scanning
• Some procedural generation process
• gear wheel generator
• maximizing/minimizing some functional (e.g.,
  minimize area as in soap bubbles)
• Some creative design process
• realizing some desired functionality
• capturing an aesthetic vision
• ( BUT NO RANDOM BLOBS ! )

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No Random Blobs !

• Many modeling systems are mostly suitable to
  make lumpy potatoes by moving dozens of control
  vertices individually.
• We will concentrate on designed shapesThese are
  optimal in some local domainany small change
  would make them inferior.

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No Warped Quadrilaterals

• A single Bézier patch or rectangular B-spline
  array does not make a solid.
• Again, there should be an element of
  DESIGN.Just randomly moving all control
  pointsis not in the spirit of CS 285.

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Make Computer (CAD) Models of

• Man-made Objects
• utensils, furniture, machinery, buildings,
  sculptures, (these may have come from CAD
  models).
• NOT complete cities, complex vehicles, ...
• Natural Objects
• mountains, sea shells, tree trunks, bones,
  (these allow some procedural generation).
• NOT animals, forests, hedges,
• Visualization Models of
• height functions, math surfaces, 4D objects,
  (these can be constructed procedurally).
• NOT fluid-flow vector fields ...

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How Do You Do Procedural Design?

• Need an Appropriate Programming Language
• Auto-LISP in AutoCAD
• Other CAD extensions
• Mathematica
• Matlab
• C,C
• SLIDE (Unigrafix, OpenGL, Tcl) gt
• For your course projects you can use whatever
  Programming/CAD environment makes you most
  productive.

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The PROs and CONs of SLIDE

• Lies between
• Mathematica / Matlab and
• Traditional CAD tools (Solidworks, Autocad)
• Offers interactive fine tuning of critical
  parameters via some sliders, gives visual
  feedback.
• Source code is under our own control.
• Not a properly maintained system.
• Tcl is a pain during the debugging process!

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Course Projects in CS 285

• See on-line list on web page ...