A path animation can use a curve-on-surface as the path curve. The workflow is identical to that when the curve is in world space; however, there is extra flexibility in controlling the “up” orientation of the object.

1. Select Create > NURBS Primitives > Plane.

   A NURBS plane appears in the scene view.

2. Select Modify > Transformation Tools > Proportional Modification Tool.

   This tool is used to introduce contours on the plane.

3. Select Modify > Make Live, and then draw a curve on the plane.
4. Select the object you want to animate along the path, and -click the curve-on-surface.

   The object and curve-on-surface are now selected.

5. Select Animate > Motion Paths > Attach to Motion Path > .

   The Attach to Motion Path Options window appears. See Animate > Motion Paths > Attach to Motion Path.

6. Ensure that either Follow or Parametric Length is on, and set the Up Direction to Normal so that the object will stay normal to the surface.
7. Do one of the following:
   • Click Attach to bind the current object to the selected curve-on-surface with the current Attach Motion Path Options.

   The Attach Motion Path Options window closes.

   • Click Apply to bind the current object to the selected curve-on-surface with the current Attach Motion Path Options.

   The Attach Motion Path Options window remains open.

   • Click Close to disregard any changes made to the Attach Motion Path Options and close the window.
     Note

     You may also wish to turn on the Inverse Up option, depending on the direction of the normals to the surface, and which side of the surface you want your object to be animated along. If you don’t know which side the surface’s normals point, you can always turn the Inverse Up option of the motion path on or off after the path animation is created.

8. Click Play in the Playback Controls to view your animation.

   You can make the animation even more complex by animating the CVs of the curve-on-surface or by creating a lattice or cluster deformer on the surface and animating this deformer object. The object animated by the path animation will stay normal to the surface at all times.

To position an object on a path

1. Select the object you want to move along the path curve.
   
2. Press the (Linux and Windows) or (Mac OS X) key to select the rotate pivot of the current object.
3. Drag the rotate pivot and position it on the object where you want it to attach to the motion path curve.
   
4. Press the (Linux and Windows) or (Mac OS X) key again to exit from the rotate pivot selection and return to object selection.

   You can now attach your object to a curve to create your path animation. See Create a motion path using a curve.

   NoteIf you forget to position the rotate pivot on your object before creating your path animation, you can always repeat these steps after the path animation has been created.

   The positioning may not seem intuitive, however, as it will appear as if the object is moving instead of the rotate pivot, as you move the rotate pivot. This is because the motion path is continually recomputing and repositioning the object so that the rotate pivot will stay on the path curve.