Tracking for CG background

# 1 31-03-2011 , 09:33 PM

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Apologies if this is the wrong forum or website completely, but It is kinda Maya related, and i reckon someone on here will have some experience with this.

I have a 3d background and I am about to shoot some actors on a green screen. The camera work will be fast and close up. I am familiar with leaving tracking markers and creating a camera solve for Maya from boujou but the issue here is that I anticipate a lack of reliable tracking data.

With a longer lens and much camera movement, my brain grinds with the prospect of creating a reliable track, knowing that only the odd marker will be in sight at any one time. I have some stands and im thinking of placing them in front and behind the actors to try and gauge any parralax and also use for tracking, but i am concerned my lovely Maya walls wont look right.

Has anyone any experience with tracking at the filming stage, i know its a bit of a longshot and apologies again if im out of line posting this on here.
thanks

James

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# 2 31-03-2011 , 11:28 PM

The Nurb Herd
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use lots of survey data i guess.

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# 3 31-03-2011 , 11:36 PM

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Thanks, i was contemplating cracking the tape measure out.

I guess i cant really be lazy with this. i suppose i could play around with dof and blur backgrounds as much as poss to hide any wobbling of cg

thanks again

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# 4 01-04-2011 , 03:25 AM

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Im not being stupid as I know SFA about film...but is the camera handheld or on a wheeled frame??? If its on a wheeled frame of some sort..you could use 2 cans of spray paint in a rig on the centreline of the camera...I use a hand operated rig painting dots on roads when setting out the paint lines. You could then draw on the ground a grid to the screen...and everywhere you take shots just...hit the button..the two cans will spray on the ground, get a lacky (mate) to ID the spots. As you will have also measured the offset from lens to can 1...can 1 to can 2 and can 2 to rear of camera...you in effect have a mobile position marker relative to the grid and screen. You could also set up a protractor or some thing similar for the vertical angle maybe??

Just an idea...might not be feasible

cheers bullet

bullet1968

"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes

Last edited by bullet1968; 01-04-2011 at 03:30 AM.

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# 5 01-04-2011 , 09:33 AM

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Tricky shot to track for sure, but remember since its close up it will be relatively forgiving on the BG since there won't be much frame of reference for the join betwee the plate and the CG so you can get away with quite alot.

Boujou is nice but not super powerful at tweaking so you have to give it quite alot to work with.

Take some survey and put some paralax stands between the actor and the wall to help get the motion right.
If you have a low depth of field it will be much easier using LEDs or bigger contrasty spherical shapes to do the tracking since corners and right angles will get blurry less steady.

If you have a spare camera shoot a static witness camera of the action and you can use that in maya to correct the main camera motion when it goes wrong. e.g. if a paralax stand goes out of shot .. your height and angle is going to slip majorly but you can shift it back into place in maya, make use of animation layers.

If you dont have any major massive turns and not enough screen space for useful paralax stands it might be easier to do a nodal track for bits of it, but really depends on the footage. Feel free to post a few movs of the footage after you've shot it and ill give you some tips.

Take a shit load of photographs of the set, and two - three witness cameras would be ideal. even a compact camera wich can go as wide as possible would help out. Just need to align them to you 3D set (model the shooting enviroment in 3D).

This kinda photography is a bit of a match move nightmare, isn't really a quick fix if you have room to get paralax do what you can! If the actors arn't moving much dont be affraid to track them either, if it will put your camera in the right place in space its better than nothing.

Also consider shooting a bit wider than you want for the final shot (10-15% extra each side) so you have more room for markers etc and then push in afterward.. or even shoot really wide and then distort and push in. Depends what your shooting on / if you can afford that much resolution loss. .. Could always strap another camera onto your main one with a wide angle lens (one of those cameras they use for sports would be fine) then just track that and parent your main camera to that in maya.

Hope thats useful

FX supervisor - double negative

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# 6 01-04-2011 , 10:03 AM

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F**k me LP you know your shit....wanna delete my post so I dont look so dumb LOL please?

bullet1968

"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes

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# 7 01-04-2011 , 10:50 AM

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good info laurie. I take it 3de would be the best thing to use for matchmove like this? Do you still do matchmove at dneg?

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# 8 01-04-2011 , 11:07 AM

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3DE does really nice single tracks and has some nice tools for controlling the solve result. Boujou is a better solver than pftrack (i think), but pf track has some decent tools for solving zooms, and the geo track makes certain kinds of shots a no brainer.

Nopes, I do FX now at dneg, using alot of houdini too which rocks user added image

FX supervisor - double negative

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# 9 03-04-2015 , 06:45 AM

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best Tracking solution!!!

If you dont have any major massive turns and not enough screen space for useful paralax stands it might be easier to do a nodal track for bits of it, but really depends on the footage. Feel free to post a few movs of the footage after you've shot it and ill give you some tips.

Take a shit load of photographs of the set, and two - three witness cameras would be ideal. even a compact camera wich can go as wide as possible would help out. Just need to align them to you 3D set (model the shooting enviroment in 3D).

This kinda photography is a bit of a match move nightmare, isn't really a quick fix if you have room to get paralax do what you can! If the actors arn't moving much dont be affraid to track them either, if it will put your camera in the right place in space its better than nothing.

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Tracking for CG background

best Tracking solution!!!

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