Autocad 2012 Tutorial

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AutoCAD 2012 Tutorial
®

Second Level: 3D Modeling

Randy H. Shih
Oregon Institute of Technology

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SDC

www.SDCpublications.com Schroff Development Corporation

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AutoCAD® 2012 Tutorial: 3D Modeling

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Chapter 3

3D Wireframe Modeling

    

Using the Setup Wizard Create Wireframe Models Apply the Box Method in Creating Models Construct with the Copy Command Understand the Available 3D Coordinates Input Options  Using the View Toolbar  Setup and Using the TRIM options

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AutoCAD® 2012 Tutorial: 3D Modeling

Introduction
The first true 3D computer model created on CAD systems in the late 1970s was the 3D wireframe model. Computer generated 3D wireframe models contain information about the locations of all the corners and edges in space coordinates. The 3D wireframe models can be viewed from any direction as needed and are in general reasonably good representations of 3D design. But because surface definition is not part of a wireframe model, all wireframe images have the inherent problem of ambiguity. For example, in the figure displayed below, which corner is in front, corner A or corner B? The ambiguity problem becomes much more serious with complex designs that have many edges and corners.

Wireframe Ambiguity: Which corner is in front, A or B? The main advantage of using a 3D wireframe modeler to create 3D models is its simplicity. The computer hardware requirements for wireframe modelers are typically much lower than the requirements for surface and solid modelers. A 3D wireframe model, also known as a stick-figure model or a skeleton model, contains only information about the locations of all the corners and edges of the design in space coordinates. You should also realize that, in some cases, it could be quite difficult to locate some of the corner locations while creating a 3D wireframe model. Note that 3D wireframe modelers are usually used in conjunction with surfacing modelers, which we will discuss in the later chapters of this text, to eliminate the problem of ambiguity. With most CAD systems, creating 3D wireframe models usually starts with constructing 2D entities in 3D space. Two of the most commonly used methods for creating 3D wireframe models are the Box method and the 2D Extrusion method. As the name implies, the Box method involves the creation of a 3D box with the edges constructed from the overall height, width and depth dimensions of the design. The 3D wireframe model is typically completed by locating and connecting corners within the box.

3D Wireframe Modeling

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The 2D Extrusion method involves making copies of 2D geometries in specific directions. This method is similar to the 2½D extrusion approach illustrated in the previous chapter (Chapter 2) with several differences. First of all, we do not really extrude the wireframe entities; instead we simply make copies of wireframe entities in the desired directions. Secondly, constructed wireframe entities have true 3D space coordinates, while the thickness approach creates entities with no true 3D coordinates. And lastly, no surfaces are created in the 3D wireframe models. In this chapter, we will illustrate the general procedure to construct a 3D wireframe model using both the box method and the 2D extrusion method. To illustrate the AutoCAD 3D construction environment, we will create the wireframe model using only the default UCS system, which is aligned to the world coordinate system. Repositioning and/or reorienting the User Coordinate System can be useful in creating 3D models. But it is also feasible to create 3D models referencing only a single coordinate system. One important note about creating wireframe models is that the construction techniques mostly concentrate on locating the space coordinates of the individual corners of the design. The ability to visualize designs in the form of 3D wireframe models is...
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