Constrain

Constrain > Aim >

Maintain Offset: Preserves the original (state prior to constraining), relative translation and rotation of the constrained object. Use this option to maintain spatial and rotational relationships between constrained objects.
Offset: Specifies an offset position (translate X, Y, and Z) for the constrained object relative to the target point. Note that the target point is the position of the target object’s rotate pivot, or the average position of the rotate pivots of the target objects. Default values are all 0.
Aim Vector: Specifies the direction of the aim vector relative to the constrained object’s local space. The aim vector will point at the target point, forcing the constrained object to orient itself accordingly. The default specifies that the object’s local rotation positive X-axis aligns with the aim vector to point at the target point (1.0000, 0.0000, 0.0000).
Up Vector: Specifies the direction of the up vector relative to the constrained object’s local space. The default specifies that the object’s local rotation positive Y-axis will align with the up vector. In turn, by default, the up vector will try to align with the world up vector. Further, by default, the world up vector will point in the direction of the world space’s positive Y-axis (0.0000, 1.0000, 0.0000).

If you define the up vector to point in the same direction as the aim vector, the constrained object will be motion history dependent. For more information, see Motion history dependence effects.
World Up Vector: Specifies the direction of the world up vector relative to the scene’s world space. Because Maya’s world space is “Y-up” by default, the default world up vector points in the direction of the world space’s positive Y-axis (0.0000, 1.0000, 0.0000).
World Up Object: Specifies that the up vector try to aim at the origin of a specified object instead of aligning with the world up vector. The world up vector is ignored. The object whose origin the up vector tries to aim at is called the world up object. You can specify the world up object with the aimConstraint MEL command (use -wuo flag). If no world up object is specified, the up vector tries to aim at the origin of the scene's world space.
Animation Layer: Lets you select an animation layer where you want to add the aim constraint. See Create aim constraints for more information.
Set Layer To Override: When on, the layer you select in the Animation Layer drop-down list is automatically set to Override mode as you add the constraint to the animation layer. This is the default and recommended mode. When off, the layer mode is set to Additive as you add the constraint. See Add constraints to animation layers for more information.

See also Animation layer modes in the Animation guide.
Constraint Axes: Determines whether the Aim constraint is restricted to a specific axis (X, Y, Z) or to All axes. When All is checked, the X, Y, and Z boxes are dimmed.
Weight: Specifies how much the orientation of the constrained object can be influenced by the target object(s). Use slider to select values from 0.0000 to 10.0000. Default is 1.0000.