Coordinates for Planar Trackers

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‌Coordinates for Planar Trackers

As with a traditional 3-D solve, you should decide where you want the camera and your 3-D planar trackers to appear in the 3-D environment. This is an artistic decision, not a technical one, as the match-move is unaffected by where you place the scene. That means that it's up to you to decide what you want! You don't have to do anything, but a good decision can make your later work easier.

For example, suppose you have tracked a rug on the floor; you want to add a logo to it. You could use a default moving-object export, and the rug mesh would be moving around in "the middle of the air," not on the ground plane. You could do the effect, though it might be a big less intuitive. (If it was a 3-D particle effect, it would not be satisfactory.)

If you switch to a moving-camera export, the rug mesh will be stationary, with the camera moving instead. But where should the rug be?

The Export Preparation has a dropdown for you to answer that question: you can select Front plane, Top (Ground) plane, Left wall, Right wall, Back, or Ceiling. (There's a little creative ambiguity in these names to be more intuitive.)

So for a rug, you probably want to select the Top(Ground) plane setting. If you tracked a window, you might choose Front, for something directly ahead you see in the front camera view, left wall for a window to the left, ceiling for something on the ceiling. Back is for something on the back of the front wall.

There's an additional setting, Camera as-is, that says to leave the stationary tracker right where it is in 3-D on the first frame of the shot, and animate the camera to evolve accordingly after that.

Note : if the 3-D planar track isn't valid on the first frame of the shot when using As-is mode, then the tracker's main frame is used as the official position of the tracker. When positioning the scene, do so on the correct frame.

When using as-is positioning, or using the moving-camera mode, you can manually pre-position the camera to any desired location, using the 3-D viewports, perspective view, and tools on the 3-D panel. For a moving-object shot, for example, you might decide that the camera was looking mainly down to the left, and adjust the 3- D camera accordingly before running the export.

You can also adjust the positioning of the camera and planar trackers as a unit after running the export preparation script. Go to the 3-D panel and click the Whole button, meaning that you want to move the entire scene.

For example, suppose you had tracked a window in a second story building, as shot from ground level. When you run Export Prep, you select the Front option. The generated scene puts the window tracker at the origin (ground level) with the correct orientation. You can then use the Whole button to move the scene upwards, so that the window is at some subjectively reasonable (but untracked and unknown) height.

The result will be a scene that will be more easy to visualize and work on, and that is the point of paying attention to the coordinates.

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