You can plot the movement of a selected point or cluster.
Setting Objects on Trajectories
Trajectories are similar to paths in that they are specialized constraints that control an animated object’s translation. Unlike a path, which interpolates an object’s position between keyframes, a trajectory’s knots serve as indicators of the object’s position at each frame. For example, if a trajectory has 18 knots, it takes only 18 frames for the object to complete its journey on the path.
A trajectory requires no keys because the object jumps from one knot to the next on the curve at each frame. This means you have absolute control as to where your object will be from frame to frame.
A situation in which you’d want to use trajectories instead of a path is when combining 3D animation with live action. You need to control the exact position of an object at each frame, which you can do with a trajectory.
You can create trajectory animation by picking an existing curve as the trajectory for an object and selecting the starting frame for the animation.
Creating a Curve by Plotting an Object’s Transformation
To quickly create a curve with the necessary knots for a trajectory, you can animate an object’s position and plot the motion of the object’s center to generate a curve. Plotting a curve helps you visualize the trajectory of an animation. You can then edit the curve to fine-tune the trajectory position for each frame.
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You can plot the movement of a selected point or cluster. |
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You can also use ghosting to view an object’s trajectory as a motion trail that is updated as the animation changes—see Ghosting Animated Objects. |
To create a curve from an animation
1. Select an object, point, or cluster whose transformation parameters are animated.
2. Choose Tools > Plot > Curve from the Animate toolbar.
3. In the Plot Curve dialog box that opens, set these options:
- The Start Frame and End Frame specify the frames at which to begin and end plotting.
- The Step Value controls the sampling of the generated curve. If this value is 1, a point on the curve is created for every frame; if this value is 2, a point is created for every other frame; and so on.
- Curve Name is the name to use for the curve that is generated from plotting the transformation.
4. When you click OK, the animation is played back and a curve is created showing the path or trajectory of the animated object. The original animation remains.
Setting an Object on a Trajectory
You can create trajectory animation by picking an existing curve as the trajectory for an object and selecting the starting frame for the animation.
To set a trajectory
1. Create a curve using any of the available tools in the Curve menu on the Model or Animate toolbars. The number of points (knots) on the curve determines how long it takes the object to complete its course on the path.
2. Select the object you want to animate.
3. Choose Create > Path > Set Trajectory from the Animate toolbar.
4. Pick the curve.
5. In the Trajectory Constraint property editor that opens, set the animation’s Start Frame.
For information on the other options in this property editor, they are the same as found in the Path constraint’s property editor — see Setting Objects on Paths.
6. Play the animation to check the results and timing.
To remove the animation, see Removing Path or Trajectory Animation.
You can either modify any values in the TrajectoryCns property editor or directly modify the trajectory curve (see Modifying the Path Curve or Trajectory).
To modify the animation
1. Select the object on the trajectory.
2. Open the TrajectoryCns property editor.
3. Change the Start Frame to change the timing or change any other value that you initially set.
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