Saturday, April 3, 2010

Camera Tracking, 3d Space and Other Stuff part 2

So I want to place that awesomely textured soda can into my scene. I can eyeball it, but that comes with a lot of trial and a lot more error as I'll demonstrate in a moment. How do we go about setting this giant can on the ground plane, or, even better (cos who doesn't like a challenge?) on the seat of the chair!

By eye:

Went to frame 100 and placed it by eye. It looks great!

see? Let's preview the motion:

Oooh. No good! Where on earth did I go wrong??? Let's look at the front view:

Now we can assume, as I italicized earlier, that each of these points touches a physical object in the scene. The can is not very close to any of them, so it now makes sense that the can appeared to fly away in that last video. There's two ways to alleviate this, easy and less easy but still easy.

The easy way to get your object to sit in the scene is to make it the child of one of the locators with no translation of it's own.

The slightly less easy way is something I find helpful in flame a lot. The reason I find it so helpful, if we're being honest, is because I haven't gotten around to learning Syntheyes' coordinate system very well so my cameras often come in super small. They work fine, but any image plane you add to the scene will be huge. So I group the camera and locators under an axis and scale them way up (generally 3000-10,000). I could still do the parenting trick, but it would upscale anything downstream and defeat the scale-up (the track would still work), so I have another way, and here it is.

learn it well, it will safe your ass one day.

Step 1: Find the locator you want your object to share space with and select it (rename it if you like) in the camera view.
Step 2: Go into an orthographic view (side, top, front--it doesn't matter), locate your desired point and place your object on it. Note which view you are in because once you've resolved the position for those two axes you don't want to touch them. In my case I was in the side view so I've resolved the Z an Y coordinates, meaning only X is left to position.

Back in camera view, pick the slider for the one unresolved coordinate, in my case X, and slide it until the object rests in the correct place according to the shot.

then you render it out, and viola!

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