Advanced Manual 3D Tracking

If the basic manual tracking procedure is not as desired, or you want to tweak your results, you can perform several procedures to make your manual 3D tracking more accurate. These procedures include the establishing of an origin, and setting references and relations between trackers.

You must establish an origin and a set of reference coordinates (x,y,z) to track the distance an object moves in space—similar to the Cartesian coordinate system where the origin is (0, 0, 0). All other track points are relative to the origin throughout the manual 3D tracking process.

NoteRemember that it is the camera that is moving and not the points in the clip.

In Action, the distance between two objects helps define the scaling of the coordinate system. The change in distance between track points for each frame in a live-action clip determines how the 3D tracker will track an object.

When changing tracking coordinate settings, you do not need to retrack the camera.

After the manual 3D tracking is computed, you can specify a coordinate system and apply it without resolving the tracking again. The camera and resulting axes are re-oriented without recomputing the tracking.

Defining Coordinates

You specify the manual 3D tracking coordinate system and point of origin in the Coordinates menu.

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The Coordinates controls are described as follows.

Enable buttonAllows you to access the Coordinates controls.

Set buttonApplies the newly entered values in the Coordinate menu. The Set button is only visible once a successful tracking has been done.

Origin boxSpecifies the track point that sets the origin of the coordinate system. This should be a point that is easy to reference in the scene such as a point in the centre of the floor or the centre of a wall.

The Origin box lists the track points you added in the Stabilizer. If you added 12 track points to the scene, track points 1 through 12 are available in the list.

Distance boxes and Is fieldSelects the track points to use for establishing the 3D tracking scale in the coordinate system. In the Is field, type a value that best represents the actual distance between the two track points selected in the Distance boxes.

To set the origin and distance:

In the manual 3D tracking controls, click Coords.

The Coordinates menu is displayed.
Click Enable to gain access to the Coordinates controls.
In the Origin box, select the track point that sets the origin of the coordinate system.
In the From box and To box of the Distance area, select the track points to use for measuring the distance and setting the 3D tracking scale for the coordinate system.
In the Is field, type a value for the distance between the From and To track points.
Because the camera distance and the field of view are directly related to the distance, consider the placement of the From and To track points with respect to the footage. Are the track points far in the back of the footage, such as on a building across a river? In this case, the value would be larger than, say, if the points were closer to the camera.

At first, you may have to try an approximate value and then experiment based on the results.

Defining Axes

You define a coordinate system to make it easier and more intuitive for inserting a virtual object or a 3D model in the scene. For example, if you want to place a 3D model on a flat surface such as a table, you should specify two coordinate directions such as coordinate X and Z, which represent the plane of that surface. The 3D tracker determines the third axis to complete the 3D coordinate system.

When specifying the two coordinate directions, such as the X-axis and Z-axis, use one common track point for both axes to establish a true coordinate system.

NoteBeware of negative and positive directions when specifying track points for the X, Y, or Z-axis. For example, if you specify points for the Y-axis, pick the track point whose Y-coordinate value is less than the second track point.

To define the axis:

In the Axes area of the Coordinates menu, set up a coordinate system by selecting one axis from the Axis1 box and another axis from the Axis2 box.

(a) Axis 1 box (b) Axis 2 box (c) Traversal Point boxes

From the Traversal Point boxes, for each axis, identify two points through which the selected axis passes.

Select:	To:
Through 2 Points	Specify the two track points through which Axis 1 or Axis 2 traverses.
From Origin To	Specify the track point through which Axis 1 or Axis 2 traverses including the origin track point.
Normal To 3 Points	Specify the three points in a plane that define the normal. The three points define the plane with which the normal is perpendicular. Use the right-hand method to determine the order.

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