You
can create realistic visual effects in a drawing by defining either
parallel or perspective projections of a model.
The
difference between perspective views and parallel projections is
that perspective views require a distance between a theoretical
camera and target point. Small distances produce severe perspective
effects; large distances produce mild effects.
The following illustration
shows the same model in both a parallel projection and perspective
projection. Both are based on the same viewing direction.
Commands3DORBIT
Rotates
the view in 3D space, but constrained to horizontal and vertical
orbit only.
DVIEW
Defines parallel projection
or perspective views by using a camera and target.
System VariablesBACKZ
Stores the back clipping
plane offset from the target plane for the current viewport, in
drawing units.
FRONTZ
Stores the front clipping
plane offset from the target plane for the current viewport, in
drawing units.
LENSLENGTH
Stores the length of
the lens (in millimeters) used in perspective viewing.
TARGET
Stores the location
(as a UCS coordinate) of the target point for the current viewport.
VIEWDIR
Stores the viewing direction
in the current viewport, expressed in UCS coordinates.
VIEWMODE
Stores the View mode
for the current viewport.
VIEWTWIST
Stores the view rotation
angle for the current viewport measured relative to the WCS.
WORLDVIEW
