How to Convert Trajectory into Spline in 3ds Max?

A tutorial guide to show how to convert a Trajectory into Spline in 3ds Max. It also covers some more useful and time saving options regarding Trajectories.

In this tutorial, I am going to show you how to convert a trajectory of an object into spline and vice versa. This tutorial will also cover some more useful options regarding trajectories that can save you a good amount of time while dealing with animation. Let’s get started!

What is a Trajectory?

Trajectory is simply defined as a path followed or created by a moving object. When we animate an object in 3ds max (or any other software) it moves according to the position it holds in 3d space for a particular frame. The path created by the movement of these objects is what we call trajectory.

For example, here, we have a box which is moving from one point to another creating a curve. Let’s take a look on how can we can convert a trajectory of an object into a spline.

Step 1

Trajectory to Spline Object

Go to Motion panel and click on Trajectories button to get access to some more options. These are some of those options that most of the people probably don’t know.

Under the Sample Range group you can specify the time period of the conversion. Once you have set the range, just click on Convert To button to convert the object’s trajectory to the spline.

In this case, the Samples value decides the number of vertices to be generated on the spline during trajectory to spline conversion.

Step 2

Spline to Trajectory

Similarly, you can convert a path or a spline object into an object’s trajectory. First, select the object then click on the Convert From button from the Trajectories rollout and pick the path / spline that you want to convert.
Delete the spline after the conversion as we don’t want it anymore.

In this case, the Sample value decides the number of keyframes to be generated on the timeline during spline to trajectory conversion.

Keyframe’s representation on a Trajectory

Keyframe's Representation

If you ever notice, keyframe is represented by a little White (for the selected object) / Red (when the object is not selected) box on the trajectory. When you make selection of keyframes, they turn Gray in color.

Transforming the Trajectory Keyframes

Turn on the Sub-Object button located at the top of the Parameters button. Now, you can move, rotate or scale these keys directly in the viewport.

Adding and Deleting Keyframes

To add keyframes to the selected object’s trajectory, just click on Add Key button and click on the trajectory.

Adding and Deleting keys

To delete Keyframes from the trajectory of an object, select the keyframes that you want to delete and click on Delete Key button or simply hit Delete on your keyboard.

How to perform Spline-Trajectory conversion with a Path Constrained Object?

The ‘spline to trajectory’ conversion doesn’t seem to work with the objects constrained to a path. Here are the two things that we can probably try if we get a path constrained object in place of a normal object.

If we have a path constrained object, we can either pick the same path that our object is constrained to OR we can leave the target path untouched and pick some other spline object instead.

However, neither of these things will work. So, what should you do to perform a ‘spline to trajectory’ conversion for a path constrained object?

Here is the solution!

Collapsing the Transform
  1. I am using path constraint with Follow option turned on. It rotates the object according to the spline as it moves along the path in the specified axis. So, in this case we got both, position and rotation of the object changing with time.
  2. For this case, we will collapse the transform of the selected object instead of picking a path. Just turn on the Position checkbox from the Collapse Transform group and click on Collapse button to perform the conversion. This will automatically include the target path into the conversion and create the position keys on the timeline.
  3. I want to collapse the position as well as rotation information of the object so I have to tick both, Position and Rotation under Collapse Transform group.

Note: Collapsing the transform will will result into the removal of animation constraints from the object.

That’s all about trajectories. I hope you have learned something new and useful from this tutorial. Let me know, if you want more short tutorials like this. Thanks!