View Full Version : Lock Down Camera or 3D track?

09 September 2009, 03:32 AM
I'm a character animator/Rigger who's been given a consulting project that requires me to deal with all aspects of visual effects creation and I have a question for anyone that has dealt extensively with integrating CG with Live Action. For the film, they've been discussing just locking down the camera for most shots with our CG character in them. My question is this, it still seems to me like finding the perspective and matching the two cameras would be a lot of work. Then in addition to that, the character still has to have shadows cast on him by live action elements and visa versa.

Would it be easier to add a tiny bit of movement to the camera and track it with a program like PFHoe? (cheap but it won't stretch our already stretched grant money:P ) In my mind, that would already give us a camera in the scene and markers for where objects (trees and the ground) would be so that we could use them as reference.

09 September 2009, 10:08 AM
If it's a locked off shot before "Action" is called you could always put a square in the frame with the corners marked, and align the bottom of a cube on that square in your 3D program. Obviously you'd remove the square once your action starts, it's just to get a reference. This should give you the proper perspective, and even the scale if you measure properly.

If it's a moving camera then the square would need to be in the frame the entire shot, and that may not work for you. In this case, just measure some straight lines and corners that you know will be picked up by the tracker later so you can set up your scene geometry.

Your scene should be completely measured so that you can rough out all the objects like tables, cabinets, etc. Keep it as simple as possible using primitives, they're only for shadow casting onto your CG .

Note: I simplified this by telling you to use a square, but you could probably shoot a cube using the same principle and get an even more accurate alignment.

09 September 2009, 10:10 AM
it easy to guestimate perspective in a locked off shot and really if you are not 100% accurate it doesn't matter as the shot is not moving and you can cheat the hell out of it.

some camera tracking apps can extract 3d camera position from a still image. But you could just do the boring thing and ACTUALLY MEASURE IT !

move the camera if you need to move the camera and then deal with the matchmove joy that comes with it. In the grand scale of making a good character which interacts and intrgrates nicely with live action footage, matchmoving is in no way the hardest task.

PS buy syntheyes its amazingly cheap and much more powerful than pfHOE.

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09 September 2009, 10:10 AM
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