Saturday, April 3, 2010

Camera Tracking, 3d Space and Other Stuff

Okay, so one of the biggest bottlenecks in doing what I consider to be high-level work is understanding camera tracking and--more importantly--what that camera tracking software gives you.

In brief, I'm going to show you how to do a simple camera track in Syntheyes and how to position shapes into that track correctly. I always felt this was relatively elementary stuff, but I've had to explain to to far to many bright people, so here we are.

We'll start with what should be a relatively easy camera track. It's easy because it has:
1. Lots of Parallax (which is to say, camera movement, not to be confused with tripod movement where the camera itself doesn't move through space.)
2. No moving objects.
3. No fast motion (twitches are generally fine, whip pans are not)
4. Lots of detail.


So I ran it through Syntheyes (hit the big green button) and got a good result. All the 3d points stick to their trackers (that's a nice giveaway if a bad track) and I'm happy with it. The only issue is that the scene isn't oriented correctly:
As you an see along the ZY orthographic view the floor is rather off angle. Easy enough fix for that, in the coordinates pane in Syntheyes.

I've noted where I put the Origin, Left/Right Coordinate (the X axis) and the (Z) Plane coordinate. For a better explanation of how this works, check out my favorite CG tutorial of all time over at the Syntheyes website.

Now we export this to Maya/Nuke/Flame/AE/Whatever. What you will get on the other end is effectively the same, and maybe this is where people fail with understanding this, but here is what you get:
-A Static Scene of points in space
-A moving camera.
That's it. It's very important to remember that the scene is static. It's also very important to remember that all the annoying locators or axes now cluttering up your scene are there for a reason. The amount of times I've seen people delete or ignore them is numerous. Coincidentally, these same people often blow what I consider to the crux of camera tracking, and this is the reason I'm spending a good piece of my afternoon writing about it. This crux being the correct spatial placement of objects in your 3d scene.

Here's the big secret: If a locator from the camera track sticks to a point on the backplate, placing an object in the same place as that locator will make it stick as well.

Basic basic stuff, I know. I also know I got in a few heated discussions with a guy who professed to be an expert at tracked cameras and I had to waste valuable time explaining why close wasn't cutting it when all his objects were hovering a foot off the ground. Turns out he was dicking with the camera and locators (which is allowable, so long as you move them as a group.) The shock.

See you in Part 2.

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