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Shot with real-world camera move in 3D scene

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James Archibald
Shot with real-world camera move in 3D scene
on Oct 2, 2015 at 10:41:48 am

Hi gang, it's been a long time - hope you're all well!

I'm no stranger to camera tracking, but up until now I've always used it to insert an effect into real footage. I'm now finding myself having to achieve the opposite. I have a completely CG backdrop created in Element (with 40 custom texture layers, incidentally! Thank god for the new Unified render mode!) and I have some fairly decent footage of my actor on a green screen with tracking marks.
I'm only using AE's own camera tracker, which I'm unconvinced was designed for this sort of situation and after much fiddling, my best efforts still leave a lot to be desired.

https://reels.creativecow.net/film/green-screen-camera-track

Ignoring the terrible keying job (WIP!) and placeholder screen content (WIP!), you can see that his feet skate across the floor creating a real disconnect from the scene. The background seems to move reeeeasssoonably accurately, but I just can't get my head around how to align a 2D layer's real camera to a 3D virtual camera. Without being able to move my actor in 3D space, I'm lost.

How would you guys go about something lke this?

Massive thanks as always,

• Archie •


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Dave LaRonde
Re: Shot with real-world camera move in 3D scene
on Oct 2, 2015 at 3:44:21 pm
Last Edited By Dave LaRonde on Oct 2, 2015 at 3:45:19 pm

You should be able to get a good track. Perhaps there'a problem with technique. How are you going about setting up the track.

And I'm not sure if you want to track or stabilize the shot. The camera doesn't move very much, so you might just want to stabilize the chroma key shot.

Mocha ought to be helpful if you're looking for a different tracking/stabilizing tool.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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James Archibald
Re: Shot with real-world camera move in 3D scene
on Oct 2, 2015 at 4:14:09 pm

Sorry for not being clear. I definitely want to keep the real-world camera movement. It's a 'studio' setup and was shot on a jib to get that floaty studio feel. I personally find it rather garish, but the character is a bit of a bellend, so it suits him to flaunt in such a way.

To get the track, I precomped him, masked out the Boom and his upper half which is quite animated. His legs remain firmly planted throughout, and I assumed that having the legs plus the tracking crosses should allow for a clean track.

It solves okay - the tracking points are where they ought to be, but when i create the tracker camera things get a bit weird. I built the 3D set with the intention of having the character at the 0, 0, 0 mark, but without being able to manipulate him in Z space, I can't figure out how to position him or the world in order to avoid floaty-feet-syndrome. It's not like I can just parent him to a 3D tracker null - he's 2D and moving independently.

I've come up with a solution in which I the 3D tracker camera I currently have, but then separately mocha-track his feet, taking the transform info from that onto a null and then using it to remove the camera move from his shot using the following expression:
p = thisComp.layer("leader").transform.position;
value + [p.valueAtTime(0)[0] - p[0],0]


Once I have him static in a frame, I bring that comp back into my 3D scene and I'm able to make him a 3D layer, effectively putting the previously tracked camera from his shot back onto him, but this time I'm able to move him in 3D to match my Element scene.

It seems like a daft workaround, but it's worked.

• Archie •


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Dave LaRonde
Re: Shot with real-world camera move in 3D scene
on Oct 2, 2015 at 6:21:20 pm
Last Edited By Dave LaRonde on Oct 2, 2015 at 6:23:39 pm

I wouldn't worry about how daft it sounds as long as it works!

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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