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Trying to parent camera rotation to a track position

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Jeremy Garchow
Trying to parent camera rotation to a track position
on Nov 29, 2010 at 8:42:27 pm

And I can't figure it out.

I have a BG plate that is one long camera pan. I have a green screen FG that is on-camera talent. I am trying to make a "faux pan" of the talent to make it seem like they were in the original scene. I figured the way to do this is make a camera and adjust the Y Rotation. It looks pretty good, meaning the pan is very believable, right up until the end when the BG pan stops. It is at this point there's a parallax shift and the BG and FG motion characteristics don't match very well.

I have tried ease in and all that, but what I really want to do is track the motion of the real pan on the BG layer and somehow apply that to an AE camera's Y rotation, making the FG layer 3D so that when the real pan of the BG slows down/stops my green screen FG will have the same characteristics. What I can't figure out is how to get the degrees of the Y rotation to match the x,y tracking of the tracker.

Any ideas would be much appreciated.

Thanks!

Jeremy


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Dave LaRonde
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:26:22 pm

[Jeremy Garchow] "...the pan is very believable, right up until the end when the BG pan stops. It is at this point there's a parallax shift and the BG and FG motion characteristics don't match very well."

I'm wondering if it's a matter of the AE camera's focal length; the default is 50mm. If you shot the pan with a zoom lens, you don't happen to recall the focal length you used, do you?

Let's say you make a 50 mm camera layer and a 200 mm camera layer. If you open their position properties, you'll note that longer-lens camera has a much greater negative-z value, which affects the motion and parallax of 3D layers at zero in z-space.



[Jeremy Garchow] "...what I really want to do is track the motion of the real pan on the BG layer and somehow apply that to an AE camera's Y rotation..."

A planar tracker like Mocha -- bundled with AE -- might do the trick for you. Its effective use is not very intuitive for the novice, as I am now discovering.

3D matchmove software like Syntheyes might also work, but it's really meant for primary camera movement, not pans.

I'd be tempted to play around with cameras of different focal lengths, apply the Y-axis animation from the original camera, and tweak the values.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Jeremy Garchow
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:29:40 pm

It's not really a lens issue, it's a motion issue. Also, I can track a point on the BG perfectly, I just don't know how to apply that track to a YRotation parameter since it's in degrees and the track is x,y points. The pan was shot on a robotic tripod head of sorts, so it slows down slowly and not uniformly. I can't get the FG to match that movement so they slow at different rates, although I can get most of the movement to match just fine.

I am going to try a different method that doesn't involve y Rotation on the camera. We'll see.

Thanks for the reply.

Jeremy


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Dave LaRonde
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:35:28 pm

If you can get a good track, is it possible in the shot's composition to apply the track to the green screen layer and forget about an AE camera?

If a track point goes off screen, you might find this handy:
http://library.creativecow.net/articles/larsen_carl/analyzing_motion.php

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Jeremy Garchow
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:37:49 pm

[Dave LaRonde] "If you can get a good track, is it possible in the shot's composition to apply the track to the green screen layer and forget about an AE camera?"

That's what I'm thinking now, just use position and parent instead of camera rotation.

What I like about the camera is it gives a little of an illusion of a real pan, with a bit of "lens distortion" like you'd see with a real camera.

I'll let you know how it goes.

Jeremy


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Dave LaRonde
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:45:19 pm

Now you got me wondering if there's a script for AE available that will transfer x-y position into camera y rotation once you know the camera's distance in z-space and focal length.

...which is what you wanted in the first place.

I don't know if it exists, but this would be a good place to check:
http://aenhancers.com/

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Graham Macfarlane
Re: Trying to parent camera rotation to a track position
on Nov 29, 2010 at 9:48:41 pm

Just an idea but if the lens/pan distortions are important couldn't you get the camera point of interest to inversly follow the tracked point? This should ensure the camera rotation matches the filmed pan at all times.
I agree with Dave though that for a comp like this a camera is not necessarily the best tool.

Graham Macfarlane
3D animator and VFX specialist
London UK


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Jeremy Garchow
Re: Trying to parent camera rotation to a track position
on Nov 30, 2010 at 5:54:10 pm

[Graham Macfarlane] "Just an idea but if the lens/pan distortions are important couldn't you get the camera point of interest to inversly follow the tracked point?"

Thanks, Graham.

Very interesting and I see what you're getting at, but I guess I can't figure the math out.

Maybe it's time to post on the expressions forum.

Jeremy


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Graham Macfarlane
Re: Trying to parent camera rotation to a track position
on Nov 30, 2010 at 8:50:14 pm

No serious math needed, Just use pickwip to make the camera target follow the tracker point first, then edit the expression with *-1

Graham Macfarlane
3D animator and VFX specialist
London UK


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Jeremy Garchow
Re: Trying to parent camera rotation to a track position
on Nov 30, 2010 at 9:08:27 pm

[Graham Macfarlane] "then edit the expression with *-1"

Right but the camera then becomes all twisted and the FG perspective is completely out of wack. I don't know, I think I might just try and keyframe it.

Thanks so much for your help.

Jeremy


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