79 Copyright Goodheart-Willcox Co., Inc. Learning Objectives After completing this chapter, you will be able to: Describe rectangular, spherical, and cylindrical methods of coordinate entry. Draw 3D polylines. Describe the function of the world and user coordinate systems. Move the user coordinate system to any surface. Rotate the user coordinate system to any angle. Use the UCS icon grips to move and rotate the UCS. Use a dynamic UCS. Save and manage user coordinate systems. Restore and use named user coordinate systems. Control UCS icon visibility in viewports. As you learned in Chapter 1, any point in space can be located using X, Y, and Z coordinates. This type of coordinate entry is called rectangular coordinate entry. Rectangular coordinate entry is the most common form of coordinate entry. However, there are actually three ways in which to locate a point in space. The other two methods of coordinate entry are spherical coordinate entry and cylindrical coordinate entry. These two coordinate entry methods are discussed in the following sections. In addi- tion, this chapter introduces working with user coordinate systems (UCSs). Introduction to Spherical Introduction to Spherical Coordinates Coordinates Locating a point in 3D space with spherical coordinates is similar to locating a point on Earth using longitudinal and latitudinal values, with the center of Earth representing the origin. Lines of longitude connect the North and South Poles and provide an east-west measurement on Earth’s surface. Lines of latitude horizontally extend around Earth and provide a north-south measurement. The origin (Earth’s center) can be that of the default world coordinate system (WCS) or the current user coordinate system (UCS). See Figure 4-1A. Understanding Three-Dimensional Coordinates and User Coordinate Systems CHAPTER 4 4
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