1. Introduction to Graphics Modeling

2. Review
What have you learnt in Fundamental of Computer Graphics (ASAS GRAFIK BERKOMPUTER)?

3. What is Geometric Modeling?
Collection of methods used to define the shape and other geometric characteristics of an object.
To construct a precise mathematical description of the shape of a real object or to simulate some process.
Embraces area of computational geometry.

4. What is Geometric Modeling? (cont.)
Special case of mathematical modeling
Visual features are very important
Geometric model – physical object

5. Geometric Data
To make pictures or design new things need a computer representation of objects.
What do we want to represent?
Shape
Appearance (color, shininess, etc.)
Material properties (density, stiffness, etc.)

6. Geometric Modeling Geometric data representation
Compute a mathematical approximation of the physical shape of an object.
Algorithms for manipulating geometry
Manipulate the variables/parameters that define the shape until we meet the objective.
Geometry creation
Interactive.
Automatic creation.

7. Applications
Computer-aided design (CAD)
Entertainment
Visualization

8. CAD
Type of design:
Conceptual design
Mechanical design
Simulation
Different type of geometric models need to be combined to produce an object.

9. CAD (cont.)
Conceptual design

10. CAD (cont.)
Mechanical design

11. CAD (cont.)
Simulation

12. Entertainment Special effects Merge real and virtual objects
Create virtual scenes indistinguishable from reality

13. Entertainment (cont.)
Animation

14. Entertainment (cont.)
Games

15. Visualization
medical
geographical
Bio-geometric

16. Requirement: CAD
Precision
Integrate additional data
Smooth surfaces

17. Requirement: Animation & Special Effects
Generality
All kinds of natural and artificial objects
Flexibility
Let animator make choices
Support high quality rendering

18. Requirement: Games Interactive Models should be small Easy to animate
User input
Rendering rate
Models should be small
Easy to animate
Procedural generation

19. Requirement: Visualization
Space efficiency
Generality
Precision
Support for fast algorithms

20. Existing Software
3D Studio MAX
Maya
Rhino3D
Lightwave

21. Applicable Mathematical Techniques
Linear algebra
Vectors
Matrix methods
Set theory
Polynomial interpolation
Numerical approximation

22. Geometric Modeling Scheme
Wireframe model
Surface model
Solid model

23. Wireframe Model
The shape of object is defined by a collection of points (vertices) and a set of edges.
Edges – line or curve connects pair of points .
Conventional approach – place the geometry entirely in the data structure.
Another approach – procedural modeling.

24. Wireframe Model (cont.)
Example:

25. Advantages of Wireframe Model
Easy to construct.
Most economical in term of time and memory requirement.
Often used previewing objects in an interactive scenario.

26. Disadvantages of Wireframe Model
Tend to be not realistic
Ambiguity
Complex model difficult to interpret
What does this object look like?

27. Disadvantages of Wireframe Model (cont.)
What object does the previous wireframe represent?
Use shading and hidden surface removal technique to improve the rendered objects.

28. Disadvantages of Wireframe Model (cont.)
Does not allow for the use of photo realistic rendering tools.
No ability to determine computationally information on mass properties (e.g. volume, mass, moment, etc.) and line of intersect between two faces of intersecting models.
No guarantee that the model definition is correct, complete or manufacturable.

29. Surface Model An area bounded by an identifiable perimeter.
In Computer Graphics – is an area within which every position is defined by mathematical method.

30. Surface Model (cont.)

31. Surface Model (cont.) Surface may be: Planar Cylindrical, conic, etc
Sculptured or freeform in shape

32. Advantages of Surface Model
To overcome ambiguity in wireframe model.
Used for generation of visually realistic images through techniques such as:
Rendering
Hidden edge removal

33. Disadvantages of Surface Model
Does not represent internal features of the model (no sense of volume).
Limited value for volumetric and mass property analysis.

34. Solid Model Most complex Complete representation
Unambiguous description
Appropriate for the world of engineering objects

35. Solid Model (cont.)

36. Step from Geometric to Program
Geometry Algebra Algorithm Program
Representation
Symbolic
Numerical
Approximation