Ch04_Outline - CHAPTER 4 3-D Solid Modeling INTRODUCTION...

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CHAPTER 4 3-D Solid Modeling INTRODUCTION The chapter outlines the most common approaches for generating 3-D computer models, in addition to how these models are viewed and modified on the computer. A particular focus is put on constraint-based modeling and its relationship to documentation, analysis, and manufacturing technologies. 4.1 MODEL DEFINITION Solid modeling is currently enjoying a considerable amount of popularity in the manufacturing industry and, for good reason, is making inroads in the educational setting. Solids modeling, because of the way it is designed, has the potential of providing a very intuitive interface to the user. Depending on the level of sophistication of the modeler, it also has the potential of allowing very complex models to be constructed. Even though wireframe models are constructed much as you would a 2-D drawing, a solid model is typically constructed much like you would the physical object. This fact can be used to allow physical models to be used to demonstrate a number of the principles of solid modeling. One of the requirements for the model tends to be that it be manifold . 4.2 PRIMITIVE MODELING A primitive modeler allows you to build models using a limited set of simple geometric forms. Using the metaphor of 'building blocks' and demonstrations with physical geometric primitives, the concept of creating more sophisticated models through purely additive means can be demonstrated. Students can typically grasp this technique of visualizing the decomposition of more complex forms into primitives quite readily, an important skill for working with modelers of all levels of sophistication. Working with purely additive techniques with primitives also allows there to be some focus on manipulation and arrangement of objects in 3-D space. Working in 3-D space on a computer screen often takes some practice. Working with primitives also gives an opportunity to focus on construction techniques used in solid modelers. One tool that some primitive modelers have is parametric control over the geometry of the primitive. A number of the more powerful solids modelers more fully incorporate parametric techniques throughout their systems to allow for variational design capabilities. 4.3 CONSTRUCTIVE SOLID GEOMETRY (CSG) MODELING This section on constructive solid geometry (CSG) introduces Boolean operations, a central tool for most of the more capable 3-D modelers. Review the figures in this section to familiarize yourself with the properties of the different Boolean operations. As is true with many concepts, the best way for students to come to understand Booleans is to do it themselves. If this is not possible, demonstrations with computer and physical models can also be effective. You may choose to begin with just union and difference and save the less used intersection operation for later. One use of demonstrating the intersection operation is that it helps drive home the fact that it is the overlap of the two bodies that is at the heart of
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Ch04_Outline - CHAPTER 4 3-D Solid Modeling INTRODUCTION...

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