CGMB214: Introduction to Computer Graphics

1. CGMB214: Introduction to Computer Graphics Topic 9 Hierarchical Modeling

2. Objectives Explain the 3 different types of model for which computer graphics is used for. Differentiate the 2 different types of entity Identify the 3 categories of model representation.

3. Basic Modeling Concepts Modeling: creation & manipulation of a system representation Model: any single representation, which is graphical or descriptive. Graphical or Geometric models are component parts of a system with entities such as lines, polygons, circles, etc.

4. Basic Modeling Concepts • Graphics can be used to create and edit the model, to obtain values for its parameters, and to visualize its behavior and structure. • Among common types of models for which computer graphics is used are: • Organization model: • hierarchies representing institutional bureaucracies. • always have various directed-graph representation • such as organization chart.

5. Basic Modeling Concepts • Quantitative models: • equations describing financial, sociological, • and mathematical systems. • often depicted by graphs or statistical plots. • graphical representation is charts, pie chart, line charts. • Geometric models: • collections of components with well-defined geometry & , interconnections between components, • including engineering and architectural structures. • always depicted by block diagrams.

6. Basic Modeling Concepts “A model is a representation of some or all of the parts of a concrete or abstract entity” • Concrete Entity: • something that physically exist, allow people to visualize and understand the structure and behavior of the entity; • also provide a convenient vehicle for experimentation with; and prediction of the effects of inputs or change to the model • e.g : cars, buildings, and circuit boards.

7. Basic Modeling Concepts • Abstract Entity : • something that does not physically exist. • e.g : management structure in a company and social group.

8. Advantages of Modelling • Models are cheap than • crashing a vehicles • building a model to test in wind tunnel. • Model are safer than • to really experience the nuclear-reactor plant malfunctions. • actual testing on passenger compartment during crashes. • What are the problems with model? • Incorrect model will not produce accurate or realistic results. • Incorrect inputs will not produce accurate or realistic results. (Garbage in, Garbage out.)

9. Geometric Models Geometric or graphical model describes components with inherent geometrical properties. Among the ingredients a geometric model may represent are: Layout and shape of components (i.e., the geometric of the entity), and other attributes affecting the appearance of the components such as color. Connectivity of components (i.e., structure of the entity) Application-specific data values and properties associated with components, such as electrical characteristics .

10. Representing Models Three-categories of model representation: • Data-based • constructed from a set of data stored (in table or linked list) • e.g. the points generated by a digitizer from a model car. • Procedure-based. • uses algorithms to transform input into predicted output. • e.g. a weather simulations that calculate variations in temperature, pressure and rainfall over time.

11. Representing Models • Mixed. • Useful models are rarely completely data-based or procedure-based. • A combination of both is common. • Two types: • Data with procedures • Data: wire-frame model of a car produced from points generated from a digitizer. • Procedure: algorithms to calculate how the points and lines would react to a simulated impact. • Procedures with Data. • Procedures: weather simulation algorithms • Data: the inputs to the simulation are real weather observations. The predicted output of the simulation is compared with the real weather observed to test the model.

12. Information representation • Information describing a model is usually provided as a combination of • geometric data • non-geometric data

13. Information representation • Geometric data • geometric information includes: • coordinate positions for locating the component parts • output primitives • attribute functions to define: • the structure of the parts • data for constructing connections between the parts.

14. Information representation • Non-geometric data • Non-geometric information includes • text labels • algorithms describing the operating characteristics of the model • rules for determining the relationship or connection.

15. Symbol Hierarchies Models can be organized as hierarchy of symbols. Symbols used to form a composite objects called modules. Group of modules will form higher-level modules. Symbols available in application modeling package are defined and structured according to the type of application the package has been designed

16. Hierarchical Modeling with Structures A hierarchical model of a system can be created with structures by nesting the structures into one another to form a tree organization.