Animating with the Channel Editor > Animation > Controlling the Speed of Objects >
Creating a Motion Path

With motion path animation, object positions follow a spline (curved line) that you create in the image window. By creating a motion path, you have a visual reference for the object's position. Use motion paths to animate the position of any of the following:

- Action—axes, light sources, camera eye, or camera point of interest, or particle manipulators. Use the Path button in the Axis and Light menus to enable or disable motion path animation for the selected axis or light. Use the Path button in the Camera menu to enable or disable motion path animation for both the camera eye and point of interest.
- Compositor—the camera or the object. The Compositor menu contains the Object and Camera buttons. Use the Object button to enable or disable motion path animation for the object. Use the Camera button to enable or disable motion path animation for the camera.
- Keyer—garbage masks for the selected axis. In the GMask menu, use the Path button to enable or disable motion path animation for the selected Keyer garbage mask.

The following procedure illustrates how to create a motion path for a 3D object (an apple) over a a 30-frame clip in Action. The 3D object follows a motion path spline that is drawn from the upper-left corner at frame 1 to the lower-right corner at frame 30.

To animate a 3D object in Action:

1. In the Axis menu, enable Path.
2. If you want to set the spline vertices automatically, enable Auto Key.
3. Move the positioner to frame 1.
4. Click the object's axis and drag the object to the upper-left corner of the image window.

   (a) The object(b) The object's axis

   TipAlternately, you can change the values of the position fields in the Axis menu.
5. If Auto Key is disabled, click Set Key.

   The first vertex on the motion path spline is created.

6. Move the positioner to frame 30.
7. Move the object to the lower-right corner of the image window.
   NoteIf you drag the object to set its second vertex, make sure you click the X-, Y-, or Z-axis and not the centre point where the three axes meet. Dragging from the centre may change the beginning keyframe of the motion path instead of setting a new keyframe.
8. Click Set Key.

   The second vertex on the motion path spline is set.

9. Scrub the positioner to view the motion path.

   (a) Motion path

10. Swipe the bar at the left or right side of the menu to view the Channel Editor.

    Once you set the second vertex, the default speed curve is created in the Channel Editor. The keyframes in the speed curve match the vertices in the motion path.

    (a) Speed curve

Spline

The spline represents the path of the object, camera, or light source, for example, and consists of alternating colour segments. Each segment represents one frame and indicates the object's speed: the longer the segment, the faster the object is travelling. When the motion path is selected, the segments of the spline are red and blue. When unselected, the segments are blue and green.

The spline is drawn using vertices. Each vertex has a tangent handle that changes the shape of the spline. Changing the shape of the spline between vertices also affects the speed of the animation.

Speed Curve

The speed curve represents the percentage of the path travelled by the animation in time. In other words, the keyframes on the speed curve correspond to the timing values for the keyframes.

The speed curve is created automatically when you draw the motion path. The speed curve controls the timing of the animation. When you create the motion path, a keyframe is added to the speed curve for each vertex on the spline. You can edit the speed curve and adjust the timing of the animation by moving, adding, and deleting vertices from the spline or keyframes in the speed curve. Modifying keyframes on the speed curve does not affect the shape of the motion path spline.