AutoCAD 2008 User's
Guide > Create and Modify
Objects > Use Precision
Tools > Use Coordinates and
Coordinate Systems (UCS) >
Specify Workplanes in 3D (UCS)
Control of the user coordinate system is essential for effective 3D modeling.
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.
Several methods are available for manipulating the user coordinate system in 3D. You can also save and restore user coordinate system orientations.
With the dynamic UCS feature, you can temporarily and automatically align the XY plane of the UCS with a plane on a solid model while creating objects.
