Target Track

Usage  |  Controls

The Target Track node is an interactive camera tracking node that can be used to track problematic shots.

The Target Track node can be considered as a cross between a feature tracker and a survey solver. Note that the Target Track node cannot estimate camera focal length, so this value must be entered into the Clip Input node before tracking.

Targets are much like feature tracks, but also have a position in 3D space, defined by their 2D tracker position on the image plane and
a distance from the camera. Targets have a minimum and maximum distance, and the target location will be adjusted within this range whilst estimating camera motion.

Usage

Targets are positioned in the image and their distance from camera initialised. Once targets have been created, they can be tracked through the clip. As each target is positioned, the camera position will be updated to match the tracker path, and tracker distances will be adjusted within their min/max ranges to reduce the projection error for each target.

Best results are obtained by positioning multiple targets in one frame, selecting all the targets from the list, and tracking one frame at a time forwards or backwards through the clip. When Auto refine is enabled, the entire camera path will be automatically refined after each tracker is adjusted.

The camera path can also be refined manually to improve the overall solution after an initial path has been generated using a few trackers, especially when combined with a camera smoothing option to smooth out the motion path.

Here is an example of four targets positioned on a static object (footage from http://www.hollywoodcamerawork.us/trackingplates.html. Their min/max distances are displayed in the viewer window using purple lines.

And here is the resulting camera path after the four targets were tracked together, one frame at a time, through the clip.

Controls

Solver

Reset: Reset the solved camera path to its default state.

Remove Key: Remove the current keyframe from the camera path.

Refine All: Refine both the camera path and 3D target positions to better fit the target paths.

Auto refine: When enabled, every adjustment to a target tracker will mean all target distances and camera positions are updated

Use hint: When enabled, the input camera path will be used as a starting guess for the camera solver.

Tracking Window: This window displays the image pattern for the first selected tracker, along with the current x and y tracker position and matching score. A matching score of 1.0 indicates a perfect match of the tracker's reference pattern and the pattern in the current frame. Tracker positions can be adjusted interactively in this window by clicking and dragging with the left mouse button. Holding the Ctrl key will provide finer-grain control over the tracker position. Also, holding down the Alt/Option key while pressing the cursor keys can be used to reposition the tracker. The tracker moves by a default 1/40 of the tracking window size with each cursor key press (adjustable in the preferences) although the cursor key can be held down to move at a faster rate and more than one cursor key can be pressed simultaneously to move diagonally. Clicking the C button will centre the current tracker around a significant tracking marker.

Camera

Focal length: The camera focal length at the current frame. Focal length can be set as Constant or Variable, and the focal length must be set before tracking.

Field of view: The horizontal and vertical field of view at the current frame, measured in Degrees.

Sensor size: The horizontal and vertical sensor/film back size. To change sensor size, edit the camera preset values in the Clip Input node.

Pixel aspect: The current pixel aspect ratio. To change the pixel aspect ratio, edit the camera preset value in the Clip Input node.

Translation: The type of camera translation and smoothing. Smoothing options are None, Low, Medium and High. Camera translation types are Normal (a freely moving camera) or None (for a camera that only rotates).

Rotation: The type of camera rotation and smoothing. Smoothing options are None, Low, Medium and High. Camera rotation types are Normal (a freely rotating camera) and None (for a camera that only translates).

Lock roll: When enabled, the camera roll (i.e. rotation around the Z axis) will be locked.

Targets

The target list contains all targets that will be used for tracking. The Base Frame indicates the frame in which the target was first placed, and is used to define the 3D target position according to the target distance.

New target: Create a new target. Select the target from the list and click in the Cinema window with the left mouse button to place the target.

All / None: Select all or none of the targets for tracking.

Lock/Unlock: Lock or unlock selected targets. Locked targets will not have their 3D position changed during refinement.

Adjust Distance: When enabled, clicking and dragging with the left mouse button in a 3D viewer window will change the distance of selected targets from the camera in their base frame.

Adjust Min: When enabled, clicking and dragging with the left mouse button in a 3D viewer window will change the minimum distance of selected targets from the camera in their base frame.

Adjust Max: When enabled, clicking and dragging with the left mouse button in a 3D viewer window will change the maximum distance of selected targets from the camera in their base frame.

Delete Target: Delete the selected targets from the list.

<<, <, >, >>: Track selected targets forwards or backwards through the clip. << or >> will track continuously until the start or end of the clip is reached, provided the tracker matching score does not drop below the failure threshold. < or > will track by one frame only.

R-, Remove Key, R+: Remove keyframes from a target. The R- button removes all keyframes from selected targets before the current frame, and R+ from after the current frame. Remove Key removes keyframes from only the current keyframe.

H-, Hide, H+: Remove a target from frames so it no longer contributes to the camera solve. This is necessary when a target is occluded by another moving object, or when the target should move out of bounds but instead is tracked to an incorrect position. Hide removes the target from the current frame. Frames in which the target is visible are displayed in dark red in the scrub bar. H- or H+ remove a target from all previous or future frames, up to the point where a manual keyframe has been positioned.

Tracking Parameters

Channels: The image channels will be used to match reference patterns. If one or more channels contains significant noise, or does not contain any useful pixel information, disabling these channels can often improve the accuracy of tracking.

Search mode: The algorithm used to perform tracking. The default value is Better Speed, which will perform a search over the search range to find the most likely match for the reference pattern, but changing this to Better Accuracy will mean that small features are found more reliably during the search.

Deformation: Allowable deformations of the pattern windows over time during tracking. By enabling Rotate, Scale and/or Skew, tracking windows can warp and deform in order to better match the reference pattern. This will slightly increase the time it takes to track, but can often mean that trackers exist for longer before their matching score drops below the failure threshold.

Window update: The frequency of reference pattern updates during tracking. The default value, Starting Frame, means the reference window is updated at the frame where tracking starts (i.e. the frame where one of the <<, <, >, >> tracking buttons are pressed). Changing this to Every Frame cause the reference pattern to be updated after every frame is tracked. This may result in a feature tracking for longer before its matching score drops below the failure threshold, but could also result in feature drift as small errors accumulate over time. The final option, Above Threshold, will only update the reference window in frames where the matching score is above the window threshold parameter.

Window threshold: The minimum matching score that a tracker can have before its reference window is updated when window update mode is set to Above Threshold. If a tracker's matching score is below this value, the reference window will be not be updated.

Failure threshold: The minimum matching score allowable before tracking is terminated. During tracking, a tracker will be rejected if its matching score falls below this value. The matching score for a tracker is displayed in the tracking window.

Tracking offset: The offset the tracking window from the actual location of the tracker. This is useful in situations where a tracker may be partially obscured, but an nearby area of the image that exhibits the same motion can be found to track instead. By offsetting the tracking window, motion from this nearby area can be used to update the tracker position. The tracking offset can be adjusted interactively in the Cinema window by holding down the Ctrl key whilst moving the tracker using the left mouse button.

Consistency: When enabled, tracking will be terminated when a tracker moves in a way that is inconsistent with motion in nearby frames.

Illumination: When enabled, local image brightness will be taken into account when tracking, so effects such as flicker or lighting changes do not reduce the overall matching score as much.

Blur: When enabled, image data will be blurred slightly before tracking. This has the benefit of limiting the effect that image noise can have on reducing the overall matching score.

Predict motion: This option is only available when metadata describing approximate camera motion is available for the clip (e.g. from gyroscopic sensors on the camera). Enabling this option will use such data to try and improve the estimate of camera motion, which can often help in situations where there would otherwise be ambiguous results due to a lack of parallax.

Reset: Reset the tracking parameters back to the current default values.

Set Default: Save the current tracking parameters as default values for newly created trackers. This can be used to avoid the need to define the same tracking parameters individually for each tracker.

Errors Graph

The error graph plots the tracking error (measured in pixels) for each tracker in each frame, along with the average tracking error for all trackers visible in a frame. The tracking error is 0.0 when the matching score for a tracker is 1.0, indicating a perfect match. Selected trackers are shown in yellow, and unselected trackers are shown in blue. The average tracking error graph is shown in white. The error graph can be translated and scaled by clicking and dragging with the right or middle mouse buttons.

Individual trackers can be selected from the graph by clicking with the left mouse button. When a tracker is selected, the current frame will change to match the frame number that was clicked in the graph. If the Centre View display option is also enabled, the Cinema window will be panned to display the tracker location in the centre.

All: When enabled, error graphs will be shown for all trackers, otherwise a graph will only be shown for selected trackers.

Fit: Scale and translate the error graph so all graphs are visible.

Coverage Panel

The Coverage Panel displays information about the frames in which each target has been tracked:

The Coverage Panel displays each target as a horizontal chart, illustrating the frames in which each target is visible. The current frame is displayed using white vertical lines.

By default, the Coverage Panel displayed keyframe information showing how targets have been positioned and tracked. Each frame in which the target is present is shown with a blue square. Yellow squares show frames in which the target was manually placed.

Frames in which the target is visible but has not been positioned are displayed in dark red. It is important to ensure that targets have been positioned in all frames in which they are visible.

Alternatively, the Coverage Panel can also display the projection error for each target point by clicking the Errors button. This switches the colour-coding of each indicator to show the error of the solved point in each frame. This is colour-coded to show green for less than 0.5 pixels error, yellow for 1.5 pixels error, and red is greater than 2.5 pixels.

Clicking on any indicator will select the target point and display that frame in the Cinema window. Holding the Ctrl key will allow multiple targets to be selected.

The panel can be panned horizontally or vertically by clicking and dragging with the right mouse button. Clicking and dragging with the middle mouse button will zoom either horizontally or vertically to increase the number of targets and frames that are displayed in the panel.

The mouse wheel can also be used to zoom horizontally, or vertically if the Alt/Option key is held.

Additional controls are also available:

All: Switch between displaying all trackers, or only those targets visible in the current frame.

Keys: Display keyframe information, showing where targets have been tracked and manually positioned.

Errors: Display projection error information.

Name: Sort the targets by name, in alphabetical order.

Start: Sort the targets according to the first frame in which they are tracked.

End: Sort the targets according to the last frame in which they are tracked.

Fit: Fit the targets display to the window. This will zoom in or out as necessary, displaying as many targets and frames as will fit in the viewport.

Display

Show Ground: When enabled, the ground plane will be displayed.

Show Horizon: When enabled, the horizon line will be displayed.

Show Geometry: When enabled, the geometric objects from up-stream will be displayed.

Show Names: When enabled, selected target names will be displayed.

Show Info: When enabled, selected target positional information will be displayed.

Show Path: When enabled, target tracker paths will be displayed.

Show Search: When enabled, target search areas will be displayed.

Centre View: When enabled, the image displayed in the Cinema window will be translated so that the first selected target is positioned in the centre of the window.

Default Keyboard Shortcuts

Keyboard shortcuts can be customised in the Preferences.

Reset Solver	Shift+E
Remove Solver Key	Shift+V
Refine All	Shift+R
Centre On Tracker	Alt/Option+C
Reset Tracking Parameters	Shift+S
Set Default	Shift+F
New Target	Shift+W
All/None	Shift+A
Lock/Unlock	Shift+L
Adjust Distance	Ctrl+D
Adjust Min	Ctrl+K
Adjust Max	Ctrl+M
Delete Target	Del
Track Backwards	[
Track Backwards Frame	Shift+{
Track Forwards Frame	Shift+}
Track Forwards	]
Remove Backwards	;
Remove Key	'
Remove Forwards	#
Hide Backwards	Shift+:
Hide	Shift+@
Hide Forwards	Shift+~
Show Ground	Ctrl+G
Show Horizon	Ctrl+H
Show Geometry	Ctrl+E
Show Names	Ctrl+N
Show Info	Ctrl+I
Show Path	Ctrl+P
Show Search	Ctrl+S
Centre View	Shift+C