Page 650 - Kitab3DsMax

Part V: Animation and Rendering Basics

LookAt constraint
The LookAt constraint won’t move an object, but it rotates the object so it is always orientated toward the
target object. For example, you could use the LookAt constraint to animate a character’s head that is watch-
ing a flying bumblebee. It is also very useful to apply to camera objects that follow a specific object through-
out the animation.
After you select a target object, a single line extends from the object and points at the target object. This
line, called the Viewline, is visible only within the viewports.
The LookAt Constraint rollout, like many of the other constraints, includes a list of targets. With the Add
and Delete LookAt Target buttons, you can add and remove targets from the list. If several targets are on the
list, the object is centered on a location between them. Using the Weight value, you can cause the various
targets to have more of an influence over the orientation of the object. The Keep Initial Offset option pre-
vents the object from reorienting itself when the constraint is applied. Any movement is relative to its origi-
nal position.
You can set the Viewline length, which is the distance that the Viewline extends from the object. The
Viewline Length Absolute option draws the Viewline from the object to its target, ignoring the length value.
The Set Orientation button lets you change the offset orientation of the object using the Select and Rotation
button on the main toolbar. If you get lost, the Reset Orientation button returns the orientation to its origi-
nal position. You can select which local axis points at the target object.
The Upnode is an object that defines the up direction. If the LookAt axis ever lines up with the Upnode
axis, then the object flips upside-down. To prevent this, you can select which local axis is used as the
LookAt axis and which axis points at the Upnode. The World is the default Upnode object, but you can
select any object as the Upnode object by deselecting the World object and clicking the button to its right.
To control the Upnode, you can select the LookAt option or the Axis Alignment option, which enables the
Align to Upnode Axis option. Using this option, you can specify which axis points toward the Upnode.
Caution
The object using the LookAt constraint flips when the target point is positioned directly above or below the
object’s pivot point. n
When you assign the LookAt constraint, the Create Key button for rotation changes to Roll. This is because
the camera is locked to point at the assigned object and cannot rotate; rather, it can only roll about the axis.
You can use the LookAt constraint to let cameras follow objects as they move around a scene. It is the
default transform controller for Target camera objects.

Orientation constraint
You can use the Orientation constraint to lock the rotation of an object to another object. You can move
and scale the objects independently, but the constrained object rotates along with the target object. A good
example of an animation that uses this type of constraint is a satellite that orbits the Earth. You can offset
the satellite and still constrain it to the Earth’s surface. Then, as the Earth moves, the satellite follows.
In the Orientation Constraint rollout, you can select several orientation targets and weight them in the same
manner as with the Position constraint. The target with the greatest weight value has the most influence
over the object’s orientation. You also can constrain an object to the World object. The Keep Initial Offset
option maintains the object’s original orientation and rotates it relative to this original orientation. The
Transform Rule setting determines whether the object rotates using the Local or World Coordinate Systems.

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