3D Data to 2D Tracker

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  02 February 2013
3D Data to 2D Tracker


I have following question:

I want to get 3D data from c4d to AE to use as tracking points for a 4-corner pin...

My setup is as follows:
I have a CG scene with an object, put in Nulls on the 4 corners of the face of the object which at first is static and later moves, Also I have a moving MoCam.

Now I export the compositing file with the four nulls and the camera to AE via the Exporter in Cinema.

In this .aec file I have the camera and the four null objects. Now these are of course 3d objects, therefore they are 3d layers... Also at the beginning the static Nulls are not moving, only the camera, which means the tracking points actually DO move...

How can I turn this around? I want to have the four nulls as 2D layers with position key frames relativ to a not moving camera so i can use a 4 corner pin to attach a picture file.

And no I sadly cannot use the 4 corner tracker because the material is black in grey... so tracking gives me very bad results...(well I'm gonna try it later lacking a better idea...) And I can't texture it either because the picture is also effected within after effects...

I could of course somehow render the 3D camera but I would still need to get the Nulls to have the same coordinates as the picture... (meaning if I manually move something to the first corner it has the 2d coordinates of 471 / 274 but the Null has 1870 / 3929 / (-1249)...

How would you solve my problem?

Thank you for your help!

  10 October 2013
If anyone is interessted... I exported the camera from c4d, made it the active camera and bam, it worked, had to put the layers to the right place in 3d space and parent them

but now i have a problem with a different project and the four corner pin again... grrrr
  10 October 2013
Working with 3d in AE is really frustrating, one of the reasons
i do not use AE much. I suppose that right click in position,
check "separate dimensions" and control-x to copy the x and y
values can be used to force a 2d layer( not tracker ) to follow
the projection(on xy plane) of a 3d layer.
  10 October 2013
Alternatively, you could use expressions to convert the 3d positions to a 2d screen position.

For example, lets say you wanted the "Upper Left" corner pin point to be bound to Null 1. You would alt-click the stopwatch and then type this:

L = thisComp.layer("Null 1");

That would force the 2-dimensional corner pin point to align to the 3 dimension position of the null. Rinse and repeat for the other 3 points.

Note: Things get wonky if the nulls go off camera
It's nice being part of the big picture, even if i'm just a pixel.
  10 October 2013
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