Focal length constraints

With the camera focal length parameter set to Variable, it is possible to set a “constant” constraint on the focal length that can be applied to a part of your sequence.

The focal length camera constraint can be of three types:

• Fixed - Uses the parameter value you provide and does not modify it.
• Initialized - Estimates the parameter value, starting from an approximate value that you provide.
• Unknown - Computes the parameter value without any input from you. This is the default.

When using a focal length constraint there are three main steps. First you create the constraint, and then you edit the constraint providing MatchMover with information on its type and value. Finally, you decide which frames use this constraint for the tracking process.

Nodal pan constraints

The nodal pan constraint fixes the optical center of the camera and limits the camera movement to rotation only. All nodal-only features (2D tracks that have no keys out of the nodal pan) are reconstructed with a median default depth.

Dolly constraints

The dolly constraint fixes the camera motion in one direction only, either along the X-, Y-, or the Z-axis.

Planar constraints

The planar constraint fixes the camera motion in two directions, either along the XY, XZ, or YZ planes.

Creating and enabling a constraint

You can create as many constraints as you like and toggle them by using the enable/disable check box in the constraint Parameters Window.

To create a new constraint:

1. Select the camera for which you want to add a constraint in the Project window or the Track window.
2. Do one of the following:
   • Select 3D Tracking > New Constraint.
   • Right-click the camera for which you want to create the constraint in the Project window to open the pop-up menu and select New Constraint.
3. Select the constraint parameter from the drop-down list in the Parameters Window.

   

4. When needed, select a Type from the drop-down list and enter the value in the Value text field.
5. In the Label text field, enter the name of the constraint.
6. Use the Enable check box to activate or disable the constraint for the required frame(s) of your sequence. See Adding frames to a constraint.
   NoteIf you choose to create a focal length constraint and the camera focal length parameter is not variable, a message box opens telling you that the camera constraint will be disabled.

The frames to which the constraint applies are shown by a colored rectangle in the Track window. The enabled constraint appears in bold in the Project window and the Track window.

Adding frames to a constraint

On creation, a constraint is not applied to any frames and you have to add frames to the constraint and enable it. MatchMover can only use the constraint when you have provided information concerning the frames to which the constraint is applied.

To do this, configure MatchMover to use the constraint on specified frames by creating a time range and adding or removing frames that use the constraint in the camera solving process.

In the Track window:

1. Select the time range for the constraint by pressing Shift+click and drag the pointer from the first frame to the last frame to include in the time range.
2. Do one of the following:
   • Select 3D Tracking > Edit Constraint > Add Frames.
   • Right-click in the Track window and select Add Frames from the pop-up menu.

The frames within the selected time range now have the camera constraint applied to them and MatchMover uses this information in the tracking process.

The constraint label appears in bold in both the Project window and Track window to show that it is enabled and it applies to the current time.

If another constraint already exists for the added frames, it is disabled automatically.

For example, you have a sequence of 400 frames and you know that there is a fixed zoom for the first 300 frames and a variable zoom for the last 100 frames. In the camera Parameters Window, set the Focal Length to variable and initialized.

You create a new focal length constraint and then define a time range from frames 0 to 300 in the Track View or in the Time Line. Using the function Add Frames, you apply the constraint to the frame sin the range. Finally, you set the Type according to your knowledge of the focal length in the constrained time range.

Deleting frames from a constraint

In the Track window:

1. Select the time range to delete from the focal length constraint by pressing Shift+click and drag the pointer from the first frame to the last frame to include in the time range.
2. Do one of the following:
   • Select 3D Tracking > Edit Constraint > Remove Frames.
   • Right-click in the Track window to show the pop-up menu and select Remove Frames.

Deleting a constraint

To delete a constraint select a constraint in the Constraint folder in the Project window or the Track window and either:

• Select Edit > Delete.
• Press the Delete key.

• Right-click a constraint in the Constraint folder in the Project window or the Track window and select Delete Constraint from the pop-up menu.