Spline Move

A spline was created on the trunk of the car and a track was created.

In the process of creating the track, the position of the spline on the trunk was adjusted

After checking the result, the spline points move from one adjustment to the next.

If you insert content, you will see a shift in the areas shown by the mouse cursor

How to remove this shift without rewriting the track

Before creating the track, the video was stabilized

You can’t judge the spline, judge the surface tool. That’s the visual representation of the track.

Also, you can use the adjust track module to compensate for any drift. Try that and let me know.

Your tracking system works like this

  1. First, a spline is created around the object

  2. The object is tracked, during which a track is created, information about which is written to the layer

  3. If the spline on the object drifts, then the surface also drifts.

  4. If the drift is small, then it can be removed through the adjust track

  5. If the drift is large, then you need to redo the track with different tracking settings.

Questions:

  1. What is a track? Is this the position of the surface in space, as well as the coordinates of the center point of the surface?

  2. Based on what data is the position of the surface relative to the position and shape of the spline determined?

Basically, you look to the surface to see how your track is going.
The track is represented by the surface, but the surface is not the tracking data. This is important to understand.
The surface is a child of the tracking data, meaning you can move and manipulate the surface to any point and it will still move relative to the track. Modifying the surface doesn’t modify the track unless you use manual track or AdjustTrack.

For example, If I track a car moving left to right, I can see the surface moving along with the car.
I can move the surface anywhere on the screen and it will still move with the car from that new position. It doesn’t change the relative movement of the track.

The spline just tells Mocha what to look for when tracking. Moving or adjusting the spline does not in any way affect the position of the tracking data or the surface.
When you track, Mocha takes the area covered by the spline and looks for that area on the next frame, then the tracked area moves the spline to the new area found. The spline is linked as a child to the tracking data unless explicitly turned off in the “link to track” options.

We cover this concept in detail with this tutorial:

That is, it turns out that the trajectory of the track is not displayed in any way on the video and its position on the video cannot be edited in any way?

Anatolii, your explanation for how our track works is not really accurate but in the most general sense.

To further clarify: The surface moves with the track, so yes, it is displayed. The track is displayed relative to where you place the surface.

The position can be edited with adjust track using the surface tool.

Watch that tutorial, it does help understand what is happening with planar tracking and Mocha specifically.

If you just need to adjust roto, you can hand adjust it and it animates with the track AND your keyframes. But the spline is not a good representation of the track, it is just where the track is looking.

The difficulty lies in understanding the track itself, in understanding how the creation of the track itself affects the surface area and shape of the spline.

Since the track is not visually displayed in the process of tracking, it seems that the spline and the surface behave according to their own laws.

This is the main difficulty for me to understand and it took me several months to start to be able to track complex objects and attach content to them.

In a future update to Mocha Pro, you can visually show the track trajectory on the video, as well as points on the track, one point on each frame. For each point to be attached to the track, and changing its position on the video in the frame, changes the track data in this frame. How it is done with standard point tracking in After Effects

Then the work of your tracking system would be much more understandable, not only for me, but also for your clients.

Have you watched the video Martin linked?

Yes, I did. The video explains what a spline is, how it works, what a surface is, how it works.

And also how to determine the quality of the track by indirect signs of the behavior of the displacement of the surface and the spline.

There is nothing about the track itself.

The track is just math. It’s not “visible” as points, the tracking data can be adjusted with the surface tool and the adjust track module.

How can a track be corrected using a surface?

You can align the surface to get the track where you need it. This does not correct the track. But adjust track does.

  1. If, after tracking, turn on the Manual Track mode, set the desired frame on the Mocha Pro timeline and start moving the surface around the corners in the video, will the track data change?

Or will the position of the surface on the video only change?

  1. Where is the track data written to? Can they be manually changed?

You need to let go of the point tracker concept and start thinking planar. The data is just relative pixel motion of a texture. Wherever you put the surface tool on that plane is where the data export is created. We translate planar data out of Mocha into set points like corner pins and the Surface Tool is the template for doing that. Moving the Surface will not change the tracking data inside of Mocha, only how it is exported to other software. Unless you’re using Manual Track and I will talk about that in a second.

The track data is internal, you can see the keyframes in the dope sheet but that’s not going to show you any points, just keyframed math variables. The “translation” tool that we use to show what that math data looks like visually is the Surface Tool.

When you use Adjust Track you can change the track and that’s it. Adjust Track is a corner pin correction that applies a transform OVER the tracking data to correct any drift. You can use manual track to animate past un-trackable areas using the Manual Track option. Manual Track is a hand animation of the surface tool and we translate that hand animated motion back into planar data via the Surface Tool. Think of the surface tool as the transformation of mathematical planar data into visual data. There are NO points to manipulate, only planes.

Planar data is relative pixel motion, not points. This is a key concept.

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