About the User Coordinate System (UCS)

The UCS is the active coordinate system that establishes the XY plane (work plane) and Z -axis direction for drawing and modeling. You can set the UCS origin and its X, Y, and Z axes to suit your needs. The UCS is useful in 2D design and essential in 3D design because it controls features that include

• The XY plane, also called the work plane, on which objects are created and modified
• The horizontal and vertical directions used for features like Ortho mode, polar tracking, and object snap tracking
• The alignment and angle of the grid, hatch patterns, text, and dimension objects
• The origin and orientation for coordinate entry and absolute reference angles
• For 3D operations, the orientation of work planes, projection planes, and the Z axis for vertical direction and axis of rotation

You can change the location and orientation of the current UCS by clicking the UCS icon and using its grips, or with the UCS command. Display options for the UCS icon are available with the UCSICON command.

Understand the UCS in 3D

When you create or modify objects in a 3D environment, you can move and reorient the UCS anywhere in 3D space to simplify your work. The UCS is useful for entering coordinates, creating 3D objects on 2D work planes, and rotating objects in 3D.

The UCS in Paper Space

You can define a new UCS in paper space just as you can in model space; however, the UCS in paper space is restricted to 2D manipulation. Although you can enter 3D coordinates in paper space, you cannot use 3D viewing commands such as PLAN and VPOINT.

Understand the World Coordinate System (WCS)

The WCS is a fixed Cartesian coordinate system. Internally, all objects are defined by their WCS coordinates, and the WCS and the UCS are coincident in a new drawing. However, it is usually more convenient to create and edit objects based on the UCS, which can be customized to suit your needs.