Up Vector

The Constraint->Up Vector command in the Actor and Motion modules allows you to control the up direction (or y-axis) of a camera or an object by using a secondary constraint object or null.

There are two reasons to control the up vector of the camera:

• To prevent the camera from flipping when it reaches a vertical axis with the interest. For example, you can produce a roller coaster-like action with the camera.
• To control the banking of the camera using a separate control path.

In the case of objects, the constraint has an effect only if the object has a Direction constraint, a Two Point constraint, or a Tangency constraint. These three constraints make the x-axis point to a constraining object: the Up Vector constraint makes the y-axis point to another constraining object. (See Constraint->Direction, Constraint->Two Points, and Constraint->Tangency.)

You can also apply an Up Vector constraint to an articulated chain. For more information, see the Constraining Joints and Effectors section of the Animating User's Guide.

Procedure

To use the Up Vector constraint in its simplest form:

1. Select the camera.
2. Choose the Constraint->Up Vector command and select the object to which you want to constrain the camera's up vector.

Using an independent object is not always the most effective way to control the up vector. If the Up Vector constraint coincides with the interest, a flip occurs on the current vertical axis.

This problem can be solved by creating the following nulls and constraints. This procedure makes the up vector follow the "point of view" of an animated object exactly, allowing you to animate the camera as you would animate any object:

1. Select an object.
2. Create three nulls:

• Place one null in front of the object.
• Place one null in the centre of the object as its "point of view."
• Place one null on the y-axis directly above the "point of view" null.

3. Make these nulls children of the object, so they follow the object's movements.
4. Select the camera and constrain it positionally (Constraint->Position) to the null in the centre of the object (the "point of view" null).
5. Select the camera interest and constrain it positionally (Constraint->Position) to the null in front of the object.
6. Select the camera, choose the Constraint->Up Vector command, and pick the null directly above the object's centre on the y-axis.
7. Animate the object as desired.

Now when the object moves, the camera's up vector is oriented correctly because it is constrained to the null above the object.

Last updated 03-apr-1998