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.
NoteBy default, when
you specify a view in 3D, it is established relative to the fixed
WCS rather than the movable UCS.
To enter coordinates relative to
the WCS
- Precede coordinate values with an asterisk
(*).
Entering @*2,0,0 specifies
a point two units in the X direction of the last point
entered relative to the WCS. Entering @2,0,0 specifies
a point two units in the X direction of the last point
entered relative to the UCS.
In practice, most coordinates are entered relative
to the UCS rather than the WCS.
To specify a new UCS with
three points
- Specify a new origin point. This is the
point (0,0,0) on the new UCS.
- Specify a point on the positive X axis
of the new UCS.
- Specify a point on the positive XY plane
of the new UCS.
To rotate the UCS around
a major axis
- Do one of the following:
- Enter a rotation angle. A common rotation
angle is 90.
CommandsUCS
Manages user coordinate
systems.
UCSICON
Controls the visibility
and placement of the UCS icon.
UCSMAN
Manages defined user
coordinate systems.
System VariablesUCSICON
Displays the UCS icon
for the current viewport or layout.
UCSVP
Determines whether the
UCS in viewports remains fixed or changes to reflect the UCS of
the current viewport.
