Trajectories

The Trajectories feature displays the path an object travels over time. This is useful for seeing at a glance how the object moves with respect to other objects in the scene during an animation without actually having to play the animation. Trajectories also lets you adjust the path directly and convert it to and from other formats.

• Select an object > Motion panel > Trajectories

Scooter following a trajectory

Note: By default, an object's trajectory is visible in the viewports only when the object is selected and Trajectories mode is active. To make the object's trajectory visible at all times, turn on the Trajectory checkbox under Display in the Object Properties dialog or on the Display panel Display Properties rollout.

Using trajectories, you can do the following:

• Display the 3D path for selected object’s position tracks.
• Insert and delete keys from the path.
• Move, rotate, and scale keys on the path.
• Convert the path to a spline object.
• Derive a new path from a spline object.
• Collapse any transform controller into editable keys.

Values under Sample Range are used in the Spline Conversion and Collapse Transform functions.

Note: You can assign the four principal Trajectories functions to keyboard shortcuts and other custom UI items. The following actions are available via Customize User Interface:

• Trajectory Add Key Mode Toggle : Enters and exits Add Key mode.
• Trajectory Delete Key : Activates the Delete Key function on a one-time basis.
• Trajectory Key Mode Toggle : Enters and exits the Keys sub-object level for direct editing of animation keys via transformation of the trajectory keys.
• Trajectory Toggle : If one or more objects are selected, this enters and exits Trajectories mode on the Motion panel.

Procedures

To display an object’s trajectory:

1. Select an animated object that moves over time.
2. Right-click the object and choose Properties.

   Trajectory is not available.

3. In the Display Properties group, click By Layer to change this button to By Object. Skip this step if By Object is already displayed.

   Trajectory becomes available.

4. Turn on Trajectory, then click OK.

   The Trajectory is displayed as a red line with white squares and dots. The white squares are keys, the white dots are in-betweens.

To add a key to a trajectory:

1. Select an object.
2. Display the trajectory by following the previous steps.
3. On the Motion panel, click Trajectories.
4. Click Sub-Object to activate Keys and enable editing.
5. Click Add Key.

   The button highlights.

6. Click the trajectory.

   Wherever you click the trajectory a key will be added.

7. Right-click the key and select Key Info from the right-click menu.

   In the Key Info dialog, you can change the In and Out values for the in-betweens on either side of the key. This allows you to use the trajectory key to create the illusion of hesitation or acceleration.

   You can click repeatedly to add many keys in this mode.

To delete a key from a trajectory:

1. Select a key on a trajectory. You can click it, or use window selection.
2. On the Motion panel Trajectories rollout, be sure Add Key is turned off.
3. On the Motion panel Trajectories rollout, click Delete Key.

   3ds Max deletes the key.

To transform keys on a trajectory:

1. Select one or more objects.
2. On the Motion panel, click Trajectories.
3. Click Sub-Object to activate Keys and enable editing.
4. Select one or more keys and use the transform tools on the Main toolbar to move, rotate, or scale the selected keys.

To set an object to use a spline as its animation path:

1. Create or open a scene that contains any object and a spline to use as an animation path.
2. Select the object and activate Trajectories mode.
3. Click Convert From and then select the spline.

   The trajectory is created from the spline and the object moves to its start point. If you play or scrub the animation at this point, the object moves along the path.

   Note: Any existing animation keys for the object will be incorporated at their current locations into the new path. So, for best results, use a non-animated object.

Interface

Sub-Object

Enables key editing. Use the Move, Rotate, and Scale transforms to change the location of a key(s) displayed on a trajectory.

Trajectories rollout

Delete Key

Deletes the selected key(s) from the trajectory.

Add Key

Adds key(s) to the trajectory. This is a modeless tool. When you click this button once, you can then add any number of keys by clicking the trajectory line in the viewport one or more times in succession. To exit Add Key mode, click the button again.

Sample Range group

Start Time/End Time

Specifies the interval for the conversion. If you're converting from position keyframes to a spline object, this is the time interval for which the trajectory will be sampled. If you're converting from a spline object to position keys, this is the interval over which the new keys will be placed.

Samples

Sets the number of samples for the conversion. When converting in either direction, the source is sampled at regular intervals, and keys or control points are created on the target object.

Spline Conversion group

Convert To/Convert From

Converts keyframe position tracks to and from spline objects. This enables you to create a spline trajectory for an object and then convert that spline to keyframes for that object's position track in order to do various keyframe-specific functions (such as applying constant velocity to the keys and normalizing the time). Or, you can convert an object's position keyframes into a spline object.

Tip: Convert To and Convert From can be used to move an object along a path without using a path constraint.

Collapse Transform group

Generates keys based on the current transformation of the selected object. You can apply this for any type of transform controller assigned to an object, but the main purpose of this function is to "collapse" a parametric transform effect, such as one generated by a Path constraint, into standard, editable keys.

Collapse

Collapses the transform of the selected object.

Position, Rotation, Scale

Specifies which transforms you want to collapse.

You must choose at least one checkbox to activate the Collapse button.