# Motion tracking round objects

I'm kind of new to motion tracking, and I need some help. I'm trying to replace the face on some footage of a LEGO minifigure. (You can see the footage in the GIF below):

So, I added tracking markers to the eyes and mouth of my minifigure, and tracked them. When I go to Reconstruction>Link Empty to Track, it makes empties in my 3D view. They look fine from the camera angle, but in 3D space, all of the empties are lined up throughout the entire frame sequence, they just wobble around instead of move in 3D space.

Since they don't move in 3D space, my new 3D face I am trying to add will not rotate with the head, instead, it just sticks there.

So, my question is, what do I need to do to do this? The face needs to rotate. The backface culling will take care of the other side of it so it isn't seen, but my tracking markers are not moving correctly, so it ruins the entire thing.

Thanks for the help in advance! =D

• You are just doing a 2D track that way, the trackers match with the pictures but have no 3D information. Look for tutorials on object tracking and object solving. (like vimeo.com/33283857)
– user1853
Commented Dec 8, 2014 at 1:33
• @poor I wasn't looking for a tutorial, I just haven't had any time to try out your answer yet to see if it works. It looks like it will, though. Thanks for it, I will vote it up, and try to test it out this afternoon. :) Commented Dec 9, 2014 at 15:36

As cegaton mentioned your current solution does not represent 3d space, because you don't have enough trackers. You can try the following workflow:

1. First enable object tracking

1. Try to track the head with 8-14 markers
2. Increase the search area of the markers, if the footage is jumpy
3. Solve your object track with a value bellow 0.6
4. Apply a camera solver constraint to the scene camera without solving it, this should show your object solution (calculated empties) in the viewport

1. Align your new face geometry to the empties (trackers) or use the trackers to pointcloud function to reconstruct the head

2. Apply an object solver constraint to the new geometry

Now your object hopefully should move properly with the empties.

• Thank you! I made some new footage with more tracking points, and tried your method and it worked. I had a minor issue with the face going rotating the opposite way, but I think I've figured that out. Commented Dec 14, 2014 at 1:57