When working in three dimensional space, you can define a UCS with its own 0,0,0 origin and orientation separate from the WCS. You can create as many user coordinate systems as you want, and then save and recall them as you need them to simplify construction of three dimensional entities.
For example, you can create a separate UCS for each side of a building. Then, by switching to the UCS for the east side of the building, you can draw the windows on that side by specifying only their x and y coordinates. When you create one or more user coordinate systems, the coordinate entry is based on the current UCS.
UCS aligned with the front wall of the house
To define a UCS, you can use any of the following methods:
Specify a new origin and points on the positive x and y axes.
Specify a new origin and point on the positive z axis.
Align the UCS with an existing entity.
Rotate the current UCS around any of its axes.
Align the UCS with its z axis parallel to the current viewing direction.
Align the UCS xy plane perpendicular to the current view.
When you define a new UCS, the UCS icon changes to indicate the origin and orientation of the new UCS.
To define a UCS by specifying a new origin and points on the positive x and y axes
Choose Tools > New UCS > 3 Point.
Specify a new original point.
Specify a point on the positive x axis.
Specify a point on the positive y axis.
Define the new UCS by selecting the origin (A), a point on the positive x-axis (B), and a point in the positive y direction (C)
Command line UCS
UCS: Manages user coordinate systems
UCSICON: Manages user coordinate systems
UCSMAN: Manages defined user coordinate systems
System Variables Reference
ERRNO: Displays the number of the appropriate error code when an AutoLISP function call causes an error that ZWCAD detects
PUCSBASE: Stores the name of the UCS that defines the origin and orientation of orthographic UCS settings in paper space only
UCSFOLLOW: Generates a plan view whenever you change from one UCS to another
UCSNAME: Stores the name of the current coordinate system for the current viewport in the current space
UCSORG: Stores the origin point of the current coordinate system for the current viewport in the current space
UCSXDIR: Stores the X direction of the current UCS for the current viewport in the current space
UCSYDIR: Stores the Y direction of the current UCS for the current viewport in the current space
UCSICON: Displays the UCS icon for the current viewport using bitcode
UCSVP: Determines whether the UCS in active viewports remains fixed or changes to reflect the UCS of the currently active viewport