CONSTRAINT

Three Points

 

The Constraint->Three Points command in the Actor and Motion modules positions an object to be constrained centrally between three constraining objects or nulls in a type of invisible triangle, and orients the object's y-axis to the normal of the plane defined by the three constraining objects. The x-axis of the constrained object is oriented toward the centre of the first constraint object you pick.

Note:

If no object is selected when you choose this command, a triangular face is automatically created with its end points attached to the constraints (each corner follows its corresponding constraint).

This constraint is useful for converting three positions from motion capture data into an orientation. When you have motion curve data for positions only, such as three points on the hips and trunk of an actor, you can infer the rotation of its body by using this constraint.

For more information about animating using constraints, see the Constraints section of the Animating User's Guide.

 

Procedure

  1. Select the object to be constrained. If no object is selected when you pick the three constraints, a triangular face is automatically created with its end points attached to the constraints (each corner follows its corresponding constraint).
  2. Choose the Constraint->Three Points command.
  3. Pick three constraining objects.

    Note:

    The order in which you select your constraining objects is important for getting the correct orientation of the constrained object. The first constraint defines the x-axis, and the three constraints together define the orientation of the plane for the y-axis.

    The constraining objects flash red as you pick them.

  4. Right-click to end the mode.

The constrained object is repositioned between the three constraining objects. Its x-axis is repositioned in the direction of the first constraining object's centre, and its y-axis is oriented to be perpendicular to the plane formed by the three constraining objects. As you move the constraining objects (one or all), the constrained object readjusts to stay properly positioned and oriented.

 

Last updated 03-apr-1998