Definition of 6DOF bodies

When the 6DOF body has been designed according to the previous chapter you must add the rigid body definition to the 6DOF Tracking page in QTM. This can be done in the following alternative methods:

1. Use the Define rigid body (6DOF) method from the Trajectory info window menu,

2. Use the Acquire Body method from the 6DOF Tracking page,

3. Use the Load Bodies option from the 6DOF Tracking page to load stored rigid body definitions from a file,

4. Use the Add Body and Add Point options from the 6DOF Tracking page to manually add a rigid body and its points.

The first two methods can be used to create a new rigid body definition based on a measurement. The latter two require that the points in the rigid body definition are known, either from prior measurement or by design.

Creating new rigid body definitions from a measurement

New rigid body definitions are most commonly created from a measurement. This is the easiest way to define the exact positions of the points for the best tracking results.

Preparations

Before creating the rigid body definition, the following should be taken into account:

• The marker labels

  If you want to be able to identify the markers, you can label them in advance. The easiest way is to record a file and label the markers before creating the rigid body definition using method I. When selecting labeled trajectories, the labels will be used for the points of the rigid body. When selecting unlabeled trajectories, the points of the rigid body will be named as the rigid body followed by a number (e.g., "My rigid body - 1").

  You can always change the labels of the points afterward by editing the rigid body definition.

• The alignment of the rigid body

  The alignment of the rigid body relative to the global coordinate axis will be used to set the orientation of the local coordinate system when defining the rigid body. This can be an easy way to set the initial orientation. When defining the rigid body from a file using method I, the first frame of the file or the selected range will be used to set the orientation.

Method I: Define rigid body (6DOF)

The Define rigid body (6DOF) method can be used to create a rigid body definition from selected trajectories in a measurement. This can be done during preview or from a file. An advantage when creating the rigid body from a file is that the rigid body points can be based on an average of multiple frames. The object is allowed to move during the recording. This way the rigid body points can be obtained from an average across many poses, making the definition less dependent on local measurement errors.

Follow these steps to create a new rigid body definition:

1. Select the trajectories associated with the rigid body in the 3D view window or the Trajectory info window.

2. Right-click on the selection and choose Define rigid body (6DOF) from the context menu. Alternatively, use the keyboard shortcuts F8 or Shift + F8. There are two options:

   • Current Frame (Shift + F8): Create rigid body definition based on marker configuration of the current frame.

   • Average of frames (F8): Create rigid body definition based on the average configuration of the markers in the current capture. The advantage of this method is that the statistics of the marker positions are taken into account. The Bone tolerance setting of the body will be based on these statistics. This option is not available when in Preview mode.

3. Specify the name of the rigid body.

The new rigid body definition is added to the Rigid bodies lists in the Project options and to the current file. The origin of the local coordinate system of the rigid body is set to the geometric center of the points included in the rigid body definition. The orientation is set to that of the global coordinate system at the current frame (when using Current Frame) or at the start frame of the file or the selected time range (when using Average of frames). You can modify the local coordinate by translation and rotation (see chapters Translate body and Rotate body) or change the reference coordinate system (see chapter Coordinate system for rigid body data).

Method II: Define 6DOF bodies using Acquire body method

The Acquire body method can be used to create a rigid body from markers that are detected during preview. Rigid bodies created using this method are added to the rigid body list in the Project Options.

Follow these steps to create a rigid body using the Acquire body method:

1. Start QTM and start a preview by clicking the New file icon .

2. Place the rigid body in the measurement volume so that the rotation of the desired local coordinate system is known in reference to the global coordinate system. One way is to place the body so that the desired local coordinate system is aligned with the global coordinate system and then the local origin can just be translated to the desired position.

3. Check that the markers on the 6DOF body do not merge in any of the cameras' 2D views.

4. Open the Project options dialog in QTM and go to the 6DOF Tracking page.

5. Click Acquire body to open the Acquire body dialog.

6. Click Acquire.

When the collection is done the new 6DOF body definition will be added to the rigid body list on the 6DOF Tracking page. The origin of the local coordinate system of the rigid body is set to the geometric center of the points included in the rigid body definition. The orientation is set to that of the global coordinate system during the acquisition. You can modify the local coordinate by translation and rotation (see chapters Translate body and Rotate body) or change the reference coordinate system (see chapter Coordinate system for rigid body data).

Adding an existing rigid body definition

Method III: Load from file

Rigid body definitions can be loaded from an XML file using the Load bodies button in the 6DOF Tracking page. This action will replace any rigid bodies present in the list with those in the file. All rigid bodies that are loaded from a file are by default enabled.

The XML file can be created by saving rigid bodies using the Save bodies button in the 6DOF Tracking page. The XML file can also be edited, for example, you can add, delete or modify rigid bodies in the file before loading it.

Method IV: Manually create a rigid body definition

You can manually add a rigid body definition to the rigid body list using the Add body button in the 6DOF Tracking page. You can then add points to the rigid body definition using the Add point button. This method can be used if you use a rigid body with know marker positions, for example one created using a 3D printer.

Editing rigid bodies

Rigid bodies and points by double clicking on a property or by using the Edit buttons (Edit color, Edit point, Edit label). For information about the properties, see chapter Rigid bodies.