Tangency

The Constraint->Tangency command in the Actor and Motion modules constrains the x-axis of an object to be tangent to a curve (path). That is, the x-axis points in the direction of the curve's slope at all times.

This constraint is particularly useful for having an object follow a path's direction, such as a roller coaster car following the tracks.

There are three ways in which you can use this constraint:

• If the object is not on a path, but is constrained to be tangent to the closest part of a curve.
• If an object is on a path and is constrained to be tangent to the curve of that path.
• If an object is on a path and is constrained to be tangent to another curve. It may be useful to have a "control" curve for the tangency which is not on the actual path. The object on the path is oriented according to the tangency of the point on the constraining curve. This corresponds to the current distance that the object is on the path. For example, if an object is at 50% of the path, it is tangent to the point at 50% of the constraining curve.

For more information on path animation, see the Animating on a Path section of the Animating User's Guide and the Path commands starting on Path->Pick Path in this guide.

Note:

You can also use this constraint in conjunction with the Up Vector constraint to define the rotation of an object around its x-axis. Otherwise, the roll around the x-axis is determined by the x-rotation of the object.

Procedure

This is the typical way to use a tangency constraint (constraining an object to be tangent to its path):

1. Create a curve to be used as the path.
2. Select the object you want to constrain to the path.
3. Choose the Path->Pick Path command and pick the curve. The object becomes "attached" to the path.
4. Make sure the object is still selected.
5. Choose the Constraint->Tangency command.
6. Pick the curve (path) to which you want to constrain the object.
   
   The constraining object flashes red.
   
   
7. Right-click to end the mode.

The constrained object's x-axis is repositioned in the direction of the slope of the curve. As the object moves along the path, its x-axis follows the curve's slope.

Last updated 03-apr-1998