About the User Coordinate System (UCS)

The user coordinate system (UCS) establishes the location and orientation of a movable Cartesian coordinate system. The UCS is an essential tool for many precision operations.

The UCS defines

• The XY plane, also called the work plane or construction 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

By default, the UCS icon appears in the lower-left corner of the drawing area for the current model viewport. The UCS in each paper space layout is displayed as a drawing triangle.

Note: A variety of color, size and style settings for the UCS are available from the UCSICON command. You can also turn it off when not needed.

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 icon changes automatically depending on the current visual style. The colorful 3D icon on the right displays when a 3D visual style is current.

Note: The UCS icon follows the traditional right-hand rule in determining positive axis directions and rotation directions.

The UCS in Paper Space

You can move and rotate the UCS in paper space on a layout; however, the UCS in paper space is restricted to 2D operations. By default, the UCS icon appears in the lower-left corner of the layout. You can change its default location with the UCSICON command.

Understand the World Coordinate System (WCS)

All objects in a drawing are defined by their coordinates in the World Coordinate System (WCS), a permanently fixed Cartesian coordinate system. The UCS is initially coincident with the WCS in new drawings. The squares in the lower-left corners of each of the icons indicates that the UCS icon is currently coincident with the WCS.