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3D Camera Tracker Perspective Problem

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andy baumgartner
3D Camera Tracker Perspective Problem
on Apr 4, 2018 at 1:28:09 am
Last Edited By andy baumgartner on Apr 4, 2018 at 1:30:21 am

Hi, I'm trying to add some 3d arrows to drone footage using the After Effects 3D Camera Tracker and a Cinema 4D export. All the points look good in AE and I have a "Average Error" of .54 pixels, but when I add some reference geometry to my scene (cad from which the physical object was created) and line it up with the track the perspective is wrong (the digital camera seems to have a wider angle and be closer than the drone). I know the reference object cad to be approximately correct.

CAD STL vs Drone Footage

Any ideas why the track is not accurate or how to fix it? Could it be the angle?


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Steve Bentley
Re: 3D Camera Tracker Perspective Problem
on Apr 4, 2018 at 2:30:58 am

There is more to a camera than the focal length (mm) setting in some packages. Check the "film" size or aperture size or "film back" size.
There are also a few cad packages that (bewilderingly) have a zoom setting AND a lens length setting. One should affect the other but not in these packages. Check also your angle of view in both AE and the Cad render.

Make sure that the CAD package rendered from the camera view and not some default view. The camera you want might not have been selected as the render camera.

Sometimes it helps to try change the camera in AE so you get close - not for rendering- but just to see what the CAD package should be shooting for and sometimes the problem will stick out when you know what you are trying to hit.

Keep in mind too that in AE higher Y numbers mean "down" and in 3D they mean "up" and that in some CAD packages Z is up and when it is, the Y (which should be the Z) is flipped.

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andy baumgartner
Re: 3D Camera Tracker Perspective Problem
on Apr 4, 2018 at 4:38:02 am

Thanks for the reply Steve, I'll check if there are any camera settings in AE.

The CAD is just an STL file (3d geometry) rendered in Cinema 4D (with the camera and reference points from After Effects), so cad rendering isn't the problem in this case. I suppose I could intentionally squish the physical geometry in Cinema 4D as a last resort, but I feel like it might look cheesy.

I'm planning on trying a different drone shot with more parallax tomorrow, maybe it will give the tracker more the work with or let me know if something else besides the angle is the problem.

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Blaise Douros
Re: 3D Camera Tracker Perspective Problem
on Apr 4, 2018 at 4:46:30 pm

I've done a few projects like this, though with flat-plane lines rather than CAD geometry rendered in C4D. Here are the key things to check:

Make sure the camera focal length and "film size" matches up, as Steve has specified. You need to specify that (by calculating the camera's horizontal Angle Of View and entering it in the 3D Camera Tracker) BEFORE you create the AE camera, so the 3D Camera Tracker generates the correct solve. You can't just change it by opening the camera's preferences after you create it.

Make sure that the track points that you grab in order to create the plane on which your 3D geometry will be tagged are correlating to the correct reference on your CAD model. So if you want the CAD model to be tagged to the ground, make sure you use track points from the ground plane, rather than the top of that factory building.

Finally, you may need to move that ground plane around in 3D space to finesse its position. I like to throw a Grid effect on it to help make sure everything is lining up correctly.

Once you've done all that, and can verify that your "ground plane" is tagged to the ground, then you can bring that into C4D and use it as a reference to set up the position of your CAD elements.

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andy baumgartner
Re: 3D Camera Tracker Perspective Problem
on Apr 4, 2018 at 7:29:41 pm

Thanks guys! Adjusting the field of view fixed it!

That's a good trick to use a grid effect.

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