CHS
UCB
“Procedural Solid Modeling” or
“Algorithms and Data Structures for
Procedural Design, Solid Modeling, and Rapid Prototyping”
Let’s review the meaning of some of these terms ...

“Solid” “Modeling” (“Procedural” …)

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UCB
CAD
Solid Modeling
CAGD (splines)
Procedural Modeling
When you spend more time programming than adjusting numbers or handles

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UCB
 Examples of solids and non-solids:
 What are the key properties of a solid?

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

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UCB
 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 (--> rendering class)

CHS
UCB
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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 Many modeling systems are mostly suitable to make “lumpy potatoes” by moving dozens of control vertices individually.
 We will concentrate on designed shapes:
These are optimal in some local domain; any small change would make them inferior.

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UCB
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 points is not in the spirit of CS 285.

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

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UCB
 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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UCB
 See on-line list on web page ...