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Object tracking using AE & C4D

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Michael Reisinger
Object tracking using AE & C4D
on May 17, 2013 at 4:13:15 am

Hey everyone,

I'm working on a shot with a stationary camera and focal length - no camera motion or zooms. The subject of the shot moves her head slightly.

The subject's motion is subtle, but it's important that the object I'm tracking to her head matches exactly. This comp exists in AE CS6.

The object I'm tracking to the subject's motion lives in C4D R12 and receives all its reflections and lighting in C4D.

I tried using AE's 3D Camera Tracker and exporting the resulting camera/null data to C4D. The export went fine, but the motion is in the camera, not the null. As far as I can tell there's no way to translate the camera motion from 3D Camera Tracker to null/object motion. Unless (hopefully) I'm mistaken.

I'd like to avoid a third application like Boujou if at all possible (limited time & $$). Is there any object tracking solution native to AE-C4D pipeline?

Thanks!


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Jeff Kay
Re: Object tracking using AE & C4D
on May 17, 2013 at 1:38:42 pm

If I understand what you are asking correctly, then you should be able to turn the 3D Camer Tracker into an expression that is modified by the movement in the null/object which will let it inherit the movement of the null/object without having to use any tracking solution.


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Michael Reisinger
Re: Object tracking using AE & C4D
on May 17, 2013 at 2:27:27 pm

Aha, thanks Jeff - I will try the expression approach ASAP. But, just to be clear ...

The results from 3D Camera Tracker do not include a moving null, only a moving camera. When I bring the 3D Camera Tracker data into C4D, I get a stationary null and a moving camera. I want a moving null. Possible?


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Jeff Kay
Re: Object tracking using AE & C4D
on May 17, 2013 at 4:10:19 pm

I guess I had it backwards, but you should be able to do the expression the other way such that the null inherits the movement of the camera.

I'm not certain if you'd want to link the null to the camera position, the focus point of the camera, some equation of both, or if there would have to be some sort of conversion coefficient. Bah, I'm just speculating at this point.


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Michael Reisinger
Re: Object tracking using AE & C4D
on May 18, 2013 at 5:40:45 am

Ok, thanks to Jeff's guidance I've figured out how to transform AE's 3D Camera Tracker into an object tracker. It requires a bit of work, and if you have another application on hand it's probably a better solution. Here's what I did:

1. Apply 3D Camera Tracker to your footage.
2. Select track points and create Null + Camera
3. Mute the newly created camera
4. Apply this expression to the null's orientation property:

lookAt(NULL POSITION, CAMERA POSITION)

5. Apply Track Motion (yeah, I know ... 2 tracking solutions involved) to your footage. Use a Track Point in the area where you want to track in your 3D (in my case C4D-based) object.
6. Apply an expression linking your null's position to the Track Point's Attach Point.
7. At the initial frame of your track, calculate the delta between the null's position and the camera's position.
8. Apply an expression to the keyframed camera position property, subtracting the delta value from each coordinate [x-dx, y-dy, z-dz]
9. Your null now MOVES!
10. You'll have to reposition the null in both AE (no big deal since the camera now automatically moves to the right spot due to the camera position expression) and in C4D (simply parent your moving null to a new null and reposition as necessary).

This worked for now, but there has to be a simpler, more elegant way to do this. I'm all ears ...


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Jeremy Bailey
Re: Object tracking using AE & C4D
on Aug 11, 2013 at 12:23:25 am

Create a 3d Camera track in AE then in C4D you can just add a null object or any object for that matter as a child to the camera and chose a different camera for your C4D render/default view


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Jeremy Bailey
Re: Object tracking using AE & C4D
on Aug 11, 2013 at 12:24:54 am

Create a tracked 3d camera in AE then export to C4D then in C4D can just add a null object or any object for that matter as a child to the camera and chose a different camera for your C4D render/default view


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