Tracking Using the Tracker Node

If you don't have access to SmartVector data or just prefer to use a familiar workflow, Nuke's Tracker node can drive grid shapes in GridWarpTracker. Tracker set up is slightly more painful, however. For simple shots, you might only need three or four tracks per grid, but creating tracking data for each vertices in the grid produces the best results.

To track the grids using Tracker:

1.   Add tracking anchors for the points in the grid you want to track. See Adding Track Anchors for more information on best practice.
2.   For each track in the Properties panel, select the type of movement the track is intended to output: translation (T), rotation (R), or scaling (S). For example, tracking a feature across the sequence and toward the camera may involve translation and scale.
3.   Track the selected features as described in Automatic Tracking or Keyframe Tracking.

It's a good idea to rename the tracks in the Properties panel with names that reflect their position in the image. For example, left_eye, right_eye, pupil, bottom_eye, top_eye, etc. This can help you assign the correct track to individual grid vertices.

Tracking can fail on some features, particularly in shots with movement or rotation. Have a look at Troubleshooting Auto-Tracks or Troubleshooting Keyframe Tracks for more information.

4.   After tracking your points successfully, right-click a vertex on the grid that corresponds to a tracking anchor and select Link to > Tracker1 and then the name of the track. For example, pupil as shown in the example.

5.   Repeat the linking process for all your tracking anchors and grid vertices.

An expression link, represented by the green arrow in the Node Graph, is created between the tracks and grid vertices so that the Tracker's translate keyframes drive the grids automatically.

6.   Play through the sequence to check that the grids follow the specified feature automatically, using the tracking information to move the individual points in both grids.

On simple shots, the grid should be accurate enough to use for warping or morphing. See Warping Shots with GridWarpTracker for more information.

For more complex shots with rapid movement or rotation, tracking might slip causing the grid to deform. Have a look at Correcting Grid Deformation for more information.