2011

Table Of Contents
Specify Workplanes in 3D (UCS)
Control of the user coordinate system is essential for effective 3D modeling.
Understand the User Coordinate System in 3D
When you work in 3D, the user coordinate system is useful for entering
coordinates, creating 3D objects on 2D workplanes, and rotating objects in
3D.
When you create or modify objects in a 3D environment, you can move and
reorient the UCS in 3D model space to simplify your work. The XY plane of
the UCS is called the workplane.
Important operations on objects in a 3D environment that depend on the
location and orientation of the UCS include the following:
Establish the workplane in on which to create and modify objects
Establish the workplane that contains the grid display and grid snap
Establish a new UCS Z axis about which to rotate objects in 3D
Determine up and down directions as well as horizontal and vertical for
Ortho mode, polar tracking, and object snap tracking
Define a 3D view directly into the workplane with the PLAN command
Apply the Right-Hand Rule
Use the right-hand rule to determine the positive axis direction of the Z axis
when you know the direction of the X and Y axes in a 3D coordinate system.
Place the back of your right hand near the screen and point your thumb in
the direction of the positive X axis. Extend your index and middle fingers as
illustrated, pointing your index finger in the direction of the positive Y axis.
Your middle finger indicates the direction of the positive Z axis. By rotating
your hand, you see how the X, Y, and Z axes rotate as you change the UCS.
You can also use the right-hand rule for determining the default positive
direction of rotation about an axis in 3D space. Point your right thumb in the
positive direction of the axis and curl your fingers. Your fingers indicate the
positive rotation direction about the axis.
566 | Chapter 17 Use Precision Tools