Tracking using the Analyzer Node

Performing Lens Correction

The Lens Correction settings in the Fine Tuning tab are the same settings that appear in the Analysis tab. You can apply lens correction before or after your initial analysis. If you make any changes after analysis, you'll need to update or refine the track. While not necessarily required, performing a lens correction may give better tracking results.

Lens Correction Mode box

Select Manual and set the Magnitude and Adjust fields if you want to apply lens correction during analysis.

Magnitude field

Displays the magnitude of lens correction. Editable.

Adjust field

Displays the level of secondary adjustment of lens correction. Editable.

Set the focal length by adjusting the perspective grid

The tracking analysis algorithm can make a best estimate of the focal length for the camera without any user input (see Analysis Settings). In order to refine the algorithm's analysis you can use a perspective-based grid to define the focal length. The focal length determined through the perspective grid is then used as part of the analysis. If you do not use this perspective grid or manually enter a value for the focal length, the algorithm guesses at an estimate of the focal length.

To set the focal length:

1. With the Analyzer object selected in the schematic, select the Analyzer 3D view from the View box.
2. From the Analysis tab in the Analyzer, select Perspective Based from the Focal Length box.

   A perspective grid appears in the view with the selected media.

   

3. While in Analyzer 3D view, drag each of the four corners of the rectangle to the desired location to form a rectangular grid. The rectangle automatically aligns to the new perspective. The Range Error, which displays the error estimate for the focal length, should be small relative to the focal length (should be less than 10% of the focal length).

   

   NoteWhen dragging one of the corner points of the rectangle, if your desired location cannot be computed (for example, if a point goes past another point on the plane), the location is remembered with a dotted line and red circle. Once you move other corners, your original location may now become viable, and the rectangle and grid align properly.

   (See Perspective Grid for specific details on placing the corner points.)

   

4. If you want to add manual trackers pre-process do so now (see Obtain better tracking results by adding manual trackers below).
5. Click the Analyze button to start the tracking.
6. When the tracking analysis is complete, click Confirm.

Focal Length box

Select Auto to let the 3D tracker calculate the camera values automatically. Select Manual to specify the values yourself. Select Perspective Based to use the perspective rectangle in the image to automatically determine the focal length of the camera.

Show Perspective button

Enable to display the grid corners in the Analyzer view.

Show Grid button

Enable to display the perspective grid in the Analyzer view.

Range Error field

Displays the error of the estimate for the focal length. Should be a small number relative to the focal length. Non-editable.

Obtain better tracking results by adding manual trackers

Add manual trackers to produce a more consistent track result. Each tracker consists of an inner reference box, which establishes the reference point for the tracking, and an outer tracker box, which follows the movement of the reference point. You can explicitly choose specific trackable features in the image (see How the Stabilizer Works).

While trackers can be added both pre- or post-processing, it is recommended to do so pre-process if there is going to be a difficult sequence to track. Add trackers post-process to improve the results of the automatic processing. If added post-process, click the Update button.

When tracking, the more track points you have in each frame, the smoother and more accurate the tracking results. As you place the trackers on the image, consider the following guidelines:

• Scatter the trackers by placing them on markings, corners, and shadows in the widest area possible. For example, avoid placing all trackers on the floor; place them on walls and other objects in the scene, as well as on the floor.
• Create a sense of depth by positioning trackers on points that lie in different planes, as well as on points located in the foreground and the background of the sequence.
• Avoid tracking points such as highlights or a point where the foreground and a background object meet, as they do not represent physical 3D points.
• Balance the number of trackers within each frame of the sequence so that as you move through the clip, some points leave the frame and other points appear in the frame. However, maintain a balance so that too many points do not leave or enter the frame at the same time.
• Avoid positioning the trackers in uniform areas or on linear edges where the track points may slide along the edge.

To add manual trackers:

1. In the Analyzer menu, click the Add 2D Tracker button.
   

   The Stabilizer module opens and automatically displays the Analyzer media

2. Click Add Tracker.

   A tracker will appear on the middle of the view.

3. Place the tracker over a trackable feature.

   Add as many as you need to improve the tracking.

   Manually added trackers will be assigned a number, incrementing from the first tracker. Manual trackers can then be selected by either:

   • Selecting them directly on the screen or,
   • Selecting the corresponding Tracker button.
4. Click Analyze.
5. Click Return when done to return to the Analyzer menu.

   The trackers will now be visible in the Analyzer view in a different color from the automatically generated trackers.