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Ch03_Outline - CHAPTER 3 Engineering Geometry INTRODUCTION...

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CHAPTER 3 Engineering Geometry INTRODUCTION Graphics is used to represent complex objects and structures that are created from simple geometric elements, such as lines, circles, and planes. Current 3-D CAD programs use these simple geometric forms to create more complex ones, through such processes as extrusion, sweeping, and solid modeling Boolean operations. Therefore, to fully exploit the use of CAD, you must understand geometry and be able to construct 2-D and 3-D geometric forms. 3.1 ENGINEERING GEOMETRY Geometry provides the building blocks for the engineering design process. Engineering geometry is the basic geometric elements and forms used in engineering design. Engineering and technical graphics are concerned with the descriptions of shape, size, and operation of engineered products. The shape description of an object relates to the positions of its component geometric elements in space. To be able to describe the shape of an object, you must understand all of the geometric forms, as well as how they are graphically produced. Complex engineering geometry is found in many engineered products, structures, and systems. 3.2 SHAPE DESCRIPTION Shape description of an object relates the positions of its component geometric elements (e.g., vertices, edges, faces) in space. Nomenclature of the component elements, the larger geometric configurations (e.g., hexagons, cubes, prisms, etc.), and the coordinate systems which describe their spatial locations are all important concepts in learning about technical graphics. 3.3 COORDINATE SPACE In order to locate points, lines, planes, or other geometric forms, their positions must first be referenced to some known position, called a reference point or origin of measurement. The Cartesian coordinate system , commonly used in mathematics and graphics, locates the positions of geometric forms in 2-D and 3-D space. A 2-D coordinate system establishes an origin at the intersection of two mutually perpendicular axes, labeled X (horizontal) and Y (vertical). The origin is assigned the coordinate values of 0,0. Values to the right of the origin are considered positive, and those to the left are negative. Similarly, values above the origin are positive, and those below are negative. The numbers assigned to each point are called coordinates where the first number is the X coordinate and the second number is the Y coordinate. A rectangle is created by using coordinate values for each corner and then drawing the connecting lines. In a 3-D coordinate system, the origin is established at the point where three mutually perpendicular axes (X, Y, and Z) meet. The origin is assigned the coordinate values of 0,0,0. A rectangular prism is created using the 3-D coordinate system by establishing coordinate values for each corner.
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The right-hand rule is used to determine the positive direction of the axes. The right-hand rule defines the X, Y, and Z axes, as well as the positive and negative directions of rotation on each axes.
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