To help the manual 3D tracker calculate relations between points, you can provide it with hints about the position and relationship of track points over several frames in a clip sequence. You establish track point relations by selecting the axes that track points have in common. Some track points can share the same Y-axis while a different set of track points can share the same X-axis value.

Define track point relations only after you obtain a result by setting up the 2D trackers and establishing a coordinate system. At that time you can experiment with a few relations and different camera properties until you are satisfied with your result.

For each track point in the scene whose coordinates you do know, you can create a point relation and specify its precision. For example, you may know the distance between these track points based on manual measurements or from a map. Create a point relation for each track point using a set of coordinates and set their Precision to variable or fixed, depending on the accuracy of the survey data. For example, two candlesticks on a table are at the same height above the table and a point relation would indicate that track points 3 and 4 share the Y-axis.

Avoid defining a point relation that has only one point and whose shared axis is Unknown as this provides little information to the 3D tracker.

You define track point relations in the Relations menu. The 3D tracker uses the enabled point relations.

To define track point relations:

1. In the 3D tracking manual controls, click Relations.

   
   

   (a) Create New button  (b) Relations box  (c) Shared Axis box  (d) Track Points column  (e) Related Points column  (f) Precision box  

2. Click Create New to add a relation to the list of relations in the Relations box.

   The first new relation you create appears in the Relation box and is enabled by default.

   As you add new point relations, select the relation in the Relation box and click Enable to define or modify the relation. Try using different track points than the ones you used when defining the coordinates.

3. In the Track Points column, select a track point and click the arrow to add it to the Related Points column.

   The number of track points that appear in this column corresponds to the trackers that are enabled in the Stabilizer.

4. In the Shared Axis box, select the axis shared by the related track points: Share X, Share Y, or Share Z.

   For the selected relation, the track points listed in the Related Points column share a common axis.

5. In the Precision box and Value field, select the value of the track point relation using one of the following precision types.

   Select:	To:
   Fixed	Keep the X or Y value that you specify in the Value field throughout the tracking. The 3D tracker does not modify this value. For example, when you select Share X, the Y value remains constant for the related points. This is the default.
   Initialised	Estimate the value of the track point starting with the initial value that you specify in the Value field.
   Unknown	Compute the value of the track points automatically with the3D tracker without specifying a value.

6. Click Enable.

   A track point can belong to several point relations: Share X, Share Y, or Share Z, but only one relation can be enabled at a time. If you try to enable a point relation that contains a track point already existing in another point relation, a message appears indicating the first point relation is disabled. For example, Relation 1 is defined by track 1 and track 2 that have a Share X relation. If you try to create another relation, Relation 2 for track 1 and track 2, you are prompted that Relation 1 will be disabled.

   NoteIf you already tracked the camera and later changed the trackers relations, you need to retrack the camera. See Analysing Manual 3D Tracks for more information.