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Motion Tracking inside of car


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#1 Phil Beastall

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Posted 10 March 2008 - 11:08 AM

For an upcoming video we're hoping to film inside of a car on green screen, so that the green can be keyed to show a variation of landscapes going by. However, as the camera is going to be moving inside the car, I was wondering what the best way to motion track the movement for the background to work properly is?

Would we shoot the green screen footage first and then try and replicate it, or will it be ideal to get motion tracking camera equipment to replicate the motion exactly?
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#2 James Steven Beverly

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Posted 11 March 2008 - 12:25 AM

Wow for something that complicated, you may a motion control camera or someone with a REAL good sense of muscle recall.

Edited by James Steven Beverly, 11 March 2008 - 12:29 AM.

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#3 James Steven Beverly

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Posted 11 March 2008 - 12:36 AM

Now if you create the background virtually you could use Matchmover or Commotion to create a virtual camera and lock it together but that would take some time. If you shot with 4 cameras locked down and created a panorama then uses a program like Stitcher to create a 360% view on a circular flat plane THEN used Matchmover to lock the motion together, create the virtual car window glass then tweaked the whole thing, it would probably give you the exact look you want.

Edited by James Steven Beverly, 11 March 2008 - 12:39 AM.

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#4 John Brawley

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Posted 11 March 2008 - 12:42 AM

For an upcoming video we're hoping to film inside of a car on green screen, so that the green can be keyed to show a variation of landscapes going by. However, as the camera is going to be moving inside the car, I was wondering what the best way to motion track the movement for the background to work properly is?

Would we shoot the green screen footage first and then try and replicate it, or will it be ideal to get motion tracking camera equipment to replicate the motion exactly?


I would have though a high end 3d tracking application like boujou would be able to do the job, especially if you can record the lens data and place some trackers on the green for parallax.

Boujou and other apps like it analyse the frame and what's moving and can usually re-build the move in 3d space, and create tracking data. The vertical lines of the car itself in relation the the screen will be a good start. It won't always do it though, and it will have trouble depending on how much motion blur there is, how well lit things are. But it is remarkable....

jb
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#5 Will Earl

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Posted 11 March 2008 - 04:46 AM

Some things to consider...

Survey of the set - this basically entails making a note of the 3D positions of certain features that will appear in the frame. Can be something simple like measuring things with a tape measure or more advanced like using a Leica to survey the set or doing a LIDAR scan.

You'd use this information to help line things up with Matchmover, Boujou, 3DE, SynthEyes. Survey data helps the camera solver figure out where it is in the scene.

The next tricky thing is going to be the environment outside the car. You may be able to get away with a 2D plate in the background - depends on the camera move. Your other options are a 360 pano(or how many degrees you need to cover), a complete 3D build outside the car , a miniatures shoot, or taking the camera move from the greenscreen shoot and appling that to a moco rig on a car (I'm sure there are rigs that are set up to do this should of thing).
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#6 Phil Beastall

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Posted 12 March 2008 - 10:17 AM

Thanks for all your responses. Really appreciate it.

Are there any other alternatives considering its low budget and we want to simply shoot both in real time - the background and foreground. Whether it means keeping the movement limited or can we replicate the shot as close as poss, and then in After Effects match the shots with motion tracking or any other clever techniques....Or shall I stop dreaming? :-p
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#7 Hugh Macdonald

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Posted 18 March 2008 - 08:54 AM

Make sure that your greenscreen is far enough away from the car to get good paralax.
Put tracking markers (a cross made of red tape is fine) on the greenscreen. If you can, make sure that they are in places where there is going to be minimal foreground cross-over. Your compositor will thank you for it later.
If the shot is wide enough that there's a good amount of the car body visible in shot too, then it should certainly be trackable in something like Boujou.
Shoot your background plates on a wider lens. Try to minimise camera shake motion blur. Your compositor will be stabilising any movement in the background plate - any sudden motion blur will look very strange when there's not the motion to go along with it. This can be a real pain to fix up.

You mentioned low budget. I guess this means that you're shooting on video...? This could be a bit more of a pain, as you won't be able to justify using as much defocus in the comp to hide the fact that you've blown the background plate up.

How big is the camera move going to be? If you're thinking something extreme (a la the long car shot in Children of Men) then I'd seriously rethink doing it GS.

As for the look of the comp - take your camera into a car and just shoot some stuff with it. People are always surprised by how dark the inside of a car should be. If you bring the inside up compared to the outside it will have the potential to look very unnatural.


All of the above is from a VFX point of view - from the various frustrations that I've had while trying to comp exactly this sort of thing (three films last year that included greenscreen car shots)
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#8 Benjamin_Lussier

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Posted 23 March 2008 - 11:28 PM

I agree with James.

4 or 5 cameras are enough to create a convincing 360o environment. It worked pretty well on War Of the worlds .

Motion control is way too cumbersome for a car sequence.

As for the tracking. Keep track of the Lense & D.O.F infos... boujou/syntheyes should do the rest.

I would not put tracking markers on the green screen is the camera rotates! Those will play lost and found as the camera moves around the car.


If the camera rotates... Id suggest you put a few markers inside the car and paint them out in post afterwards. That would garantee a solid track. U cant please everyone...compositors wont like you, but the matchmoving tech will be ur new best friend.
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#9 Joe Giambrone

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Posted 26 July 2008 - 07:25 PM

"Are there any other alternatives considering its low budget and we want to simply shoot both in real time - the background and foreground."

If it's "low budget," then with all due respect, I wouldn't be attempting what you describe. There's nothing wrong with locking camera for each shot, and using the same angle, lens, position info to shoot a suitable background plate. Why exactly does the camera need to move a non-moving car?
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#10 Joe Giambrone

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Posted 26 July 2008 - 07:26 PM

deleted

Edited by joegiambrone, 26 July 2008 - 07:28 PM.

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#11 Saul Rodgar

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Posted 26 July 2008 - 08:26 PM

"Are there any other alternatives considering its low budget and we want to simply shoot both in real time - the background and foreground."

If it's "low budget," then with all due respect, I wouldn't be attempting what you describe. There's nothing wrong with locking camera for each shot, and using the same angle, lens, position info to shoot a suitable background plate. Why exactly does the camera need to move a non-moving car?


That would be my suggestion as well. One thing is to like to challenge oneself and the other is to set oneself some very high standards or goals, especially when the budget doesn't allow for it.

Last year I was privvy to the set ups for a multimillion dollar stereoscopic/ 3D RED-shot road movie that shall remain nameless. There are extensive car dialogue scenes that were done on-stage with green screen backgrounds, but the camera was locked down for all of it, as far as I know. At some point there was talk of doing motion control for the inside-the-car scenes, but they were ultimately scrapped. There were too many scenes to nail down, they had the added problem of 3D/ green screen rotoscoping, etc. and they were dealing with RED as well, so it probably was enough to handle as it was. It goes to show that even big-budget movies shy away from the massive challenge this kind of situation poses.

Actually, I would do it both ways, (motion tracking and locked shots inside the car), that way you can always try to achieve the motion tracking and should the compositing not work out for whatever reason, you at least have the locked shots to fall back on. ;)
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