Chapter 4 CAD Commands and Functions 121
you to dynamically change the view. Yet other
programs have both of these options and more.
However, the basic goal of all of these functions
is the same. You need to “rotate” the point from
which you are viewing the model to better see
another part or feature on the object. The object
in Figure 4-22A is shown from a preset isomet-
ric viewing point. In Figure 4-22B, however, a
dynamic viewing command was used to rotate
the viewpoint.
AutoCAD Example:
Command: 3dorbit↵
Press ESC or ENTER to exit, or right-click to display
shortcut-menu.
(Using the cursor, pick and drag to change the view;
press
[Esc]
to exit the command.)
Command:
User Coordinate Systems
As discussed earlier in this chapter, user
coordinate systems are very helpful in 3D draw-
ing. A user coordinate system (UCS) allows the
drafter to orient the current drawing plane so
that it is parallel to a surface, such as an object
surface or feature. The XYZ drawing axes
remain oriented at 90° angles, but the drawing
plane rotates to match the orientation desired.
This is very useful when creating a 3D model,
because the model may have many features that
lie on different surfaces. Each time you need to
construct features on a different surface, you can
create a new UCS to establish a different draw-
ing plane in 3D space.
InatypicalCADprogram,theUCS command
is used to establish a user coordinate system.
After entering the command, coordinates for the
UCS origin are entered or picked and the orien-
tation of the drawing axes is specified. Points are fi
then located along the XYZ axes in relation to
the new UCS origin. In most programs, a UCS
icon is displayed in 3D drawing views to identify
each coordinate axis and the origin location. This
helps the user visualize the drawing orientation
when creating objects and changing views.
An example of using a UCS in 3D modeling
is shown in Figure 4-23. The solid model shown
includes a large hole feature on an inclined sur-
face. To simplify construction of this feature, a
UCS is created to establish a drawing plane on
the inclined surface. A solid cylinder is then
drawn with its base parallel to the surface so
that it can be used to “drill” the hole feature.
The original coordinate system is shown in
Figure 4-23A. In this system, the XY drawing
plane is parallel to the base of the object. This sys-
tem was used to construct the two holes in the
base. Notice the orientation of the XYZ axes and
the corner location of the origin. In Figure 4-23B,
the UCS is moved to the inclined surface and the
cylinder is drawn. The origin selected for the
UCS is a corner on the inclined surface. The
diameter and height of the cylinder are deter-
mined by the dimensions of the hole feature. In
Figure 4-23C, the cylinder is moved “down”
along the Z axis so that the base of the object
establishes the depth of the drill. The completed
model after removing material with the cylinder
is shown in Figure 4-23D.
The
UCS
command normally provides
options for rotating the UCS about one of the
axes to a different orientation and aligning the
UCS to an object face. In some programs, the UCS
can also be dynamically moved to a temporary
drawing location without changing the UCS
defi This allows you to quickly draw 3D finition.
objects on existing surfaces without changing
the UCS each time.
AutoCAD Example:
Command: ucs↵
Current ucs name:
*current*
Specify origin of UCS or
[Face/NAmed/OBject/Previous/View/World/X/Y/Z/
ZAxis] World:
(enter coordinates or pick a point
on screen, such as an object corner)
Specify point on X-axis or Accept:
(enter
coordinates, pick a point along the X axis, or press
[Enter]
to accept the orientation shown)
Specify point on the XY plane or Accept:
(enter
coordinates, pick a point along the Y axis, or press
[Enter]
to accept the orientation shown)
Command:
3D Animation and
Rendering Commands
As previously discussed, CAD programs
that have 3D drawing capability generally
have a command that allows you to create a