Chapter 1 Introduction to Three-Dimensional Modeling 3 Copyright Goodheart-Willcox Co., Inc. Right-Hand Rule of 3D Drawing Right-Hand Rule of 3D Drawing In order to effectively draw in 3D, you must be able to visualize objects in 3D space. The right-hand rule is a simple method for visualizing the 3D coordinate system. It is a representation of the positive coordinate values in the three axis directions. The AutoCAD world coordinate system (WCS) and a user coordinate system (UCS) are based on this concept of visualization. To use the right-hand rule, position the thumb, index fi nger, and middle fi nger of your right hand as shown in Figure 1-3. Imagine that your thumb is the X axis, your index fi nger is the Y axis, and your middle fi nger is the Z axis. Hold your hand in front of you so that your middle fi nger is pointing directly at you, as shown in Figure 1-3. This is the plan view of the XY plane. The positive X axis is pointing to the right and the positive Y axis is pointing up. The positive Z axis comes toward you and the origin of this system is the palm of your hand. The concept behind the right-hand rule can be visualized even better if you are sitting at a computer and the AutoCAD drawing window is displayed. Make sure the current drawing is based on the acad.dwt template. If the UCS icon is not displayed in the lower-left corner of the screen, turn it on by using the UCSICON command, or Figure 1-2. A—The points making up a 2D object require only two coordinates. B—Each point of a 3D object must have an X, Y, and Z value. Notice that the first two coordinates (X and Y) are the same for each endpoint of a vertical line. A B 0,4 6,4 0,4,1 6,4,1 6,4,0 6,2,0 4,2,0 4,0,0 2,0,0 0,0,0 2,0,1 4,0,1 0,2,0 0,2,1 2,2,1 4,2,1 6,2,1 6,2 4,2 2,2 0,2 0,0 2,0 4,0 X Y Z Figure 1-3. Positioning your hand to use the right-hand rule to understand the relationship of the X, Y, and Z axes. UCSICON Ribbon View Viewport Tools UCS Icon Type UCSICON