Trajectory Tangents allow to manipulate the trajectory curve in the scene. By manipulating the tangent handles, you can change the spacing of the moving object’s trajectory without needing to insert additional keyframes in between.

The Tangents are represented by the blue lines connected to the dark-green keyframe points, with small spheres at the end of each line. These blue lines are the tangent handles, which control the direction angle of the trajectory before and after a keyframe.

To manipulate the tangents, turn on the Trajectory Edit Mode. The tangents can be accessed when the Tangents icon on the Toolbar is active:

The Tangents (edit mode only) parameter in the Trajectory Tool section in the Scene Settings tab replicates the same functionality.

Editing Tangents

To select the tangent handle, click on the sphere at the end of the blue tangent line with the Left Mouse Button.
To include additional tangent handles in the current selection, Shift + Left Mouse Button the tangent controllers.

The tangent handles can be moved in Global and Local modes, just like other objects.
In the Local mode, you can move the tangent handle on the X-axis to “compress” the trajectory spacing.

Edited tangents are marked by the red dots on the keyframes on the Animation Track that belong to the object you’re editing the trajectory of:

Such tangents can be reset by clicking the Reset Tangents button:

Alternatively, you can right-click the tangent handle and select Reset tangent from the drop-down menu:

There is also the Link tangents option:

When it is enabled, moving one of the tangent handles attached to a keyframe would move the other along with it.
By disabling it, you can edit both tangent handles separately.

The Link tangents parameter in the Trajectory Tools section of the Scene Settings tab replicates the same functionality.

Limitations

There are some limitations on how and when the objects can render the tangents on their trajectory:

1. Kinematics on the interpolated interval must be set to IK.
The Tangents will not appear if the kinematics are set to FK, GR, or the “Enforce FK in interpolation” bool (in the Point controller’s “Point IK FK settings” behavior) is active.

2. Interpolation must be set to one of the Bezier types - Bezier, Bezier Viscous, or Bezier Clamped.
Linear, Step, and Fixed interpolations don’t render the Tangents. Additionally, the tangents appear only in the interpolated intervals at least one frame in length.

3. Tangents appear on the Translation and Direction trajectories only.
They don’t appear and don’t work on the Rotation trajectories.

4. Not all objects can render Tangents by default.
Here are some of the examples of character rig objects that can render Tangents on the specific trajectories:

• Translation trajectories:
  • Main Point controllers of the Pelvis, Hand, Foot, Toe.
  • Additional and Directional Point controllers of the Toe.
• Direction trajectories:
  • Main Point controllers of the Chest, Neck, Head, UpperArm, LowerArm, Calf.
  • Additional and Directional Point controllers of the Stomach, Chest, Clavicle, Hand, Head.

Rendering Trajectory Tangents

The default internal node logic of some objects doesn’t allow rendering editable Tangents on their trajectory. However, these Tangents can be rendered and used if you change some specific settings.

By default, most objects 'allow' editing their trajectory' tangents if they interpolate in Global space. Subsequently, one would need to change a specific setting to switch their interpolation from Local to Global space.

For Transform objects (Meshes, Joints, Cameras, Locators etc.), the tangents are rendered if the IK setting in the Node3D behavior is turned on:

 For Box Controllers, the tangents are rendered if the IK behavior setting in the Box_IK behavior is turned on:

For Limb Direction Controllers, the tangents are rendered if the Fix position setting in the Limb direction data behavior is turned on:

As for the Point Controllers, we recommend using whatever trajectories - Translation or Direction - work with the specific point controllers you’re editing. You can find a list of these Point Controllers at the start of the Limitations section above.

See Also

Trajectories

Timeline

Point Controllers

Box Controllers

Direction Controllers