Calculating 6DOF data

When 6DOF tracking is activated, QTM attempts to identify the measured rigid bodies from the 3D data. It is done by comparing the distances between points in the 6DOF body definitions to all distances between the computed markers’ locations. The following rules are used for calculation of 6DOF data.

• For a marker to be included in the 6DOF body none of the distances to the other markers in the body may exceed the Bone tolerance.

• When the trajectories have been identified the tracker computes the location and orientation of each measured rigid body in the coordinate system of the motion capture. The 6DOF tracker will automatically move trajectories that are outside the Bone tolerance to the unidentified labels. This is done in RT as well on tracking a file.

  • If you have identified trajectories manually in a file the 6DOF calculation will try to use all of the data, and then there will be no 6DOF data in frames where a marker is outside the tolerance. To make the 6DOF calculation remove the data outside the tolerance you can activate the Reidentify all body markers option while reprocessing, see below.

• A rigid body with sequentially coded active markers, such as the active Traqr, uses only the ID and not the Bone tolerance to identify the markers.

• The 6DOF data is only calculated if the 6DOF body residual is less than the Max residual.

• If there are frames when there are less than three markers that can be tracked on the 6DOF body, the 6DOF tracking function cannot calculate the 6DOF body in those frames.

• Each 6DOF body definition can just have one solution in the measurement, but the 3D trajectory can be included in several 6DOF bodies as long as the 6DOF definition is the same and the body points have the same names.

• When a Filter preset has been selected, the 6DOF data will be smoothed according to the preset parameters both in real time and in a capture, see chapter Smoothing 6DOF data.

The 6DOF data can be recalculated in a capture file. This is because each 6DOF body consists of labeled trajectories, from which the 6DOF data is calculated. This means that if the 6DOF data is wrong you can look at the 3D data to find the problem. To edit the 6DOF data just change the 3D data of the labeled trajectories and then reprocess the file with only the Calculate 6DOF option activated. Then QTM will recalculate the 6DOF data from the available 3D data.

When reprocessing a file the 6DOF data is reprocessed in the following ways depending on the processing steps.

• Calculate 6DOF without the Reidentify all body markers option

  • Data in all of the 6DOF labels
    When there are data in all of the labeled trajectories for the 6DOF body, then the 6DOF data is calculated directly from that data. QTM does not try to identify any other trajectories.

  • At least 3 6DOF labels with data
    If at least 3 6DOF labels contains data then QTM will calculate the 6DOF data from those and not try to identify the rest of the labels

  • Less than 3 6DOF labels with data
    When less than 3 labels in the 6DOF body is empty, then QTM will try to identify the 6DOF body again. Which means that the identified trajectories will be unidentified and the body calculated from scratch.

• Calculate 6DOF with the Reidentify all body markers option

  • All cases
    With the reidentify option the reprocessing will try to reidentify all of the markers in the 6DOF bodies. Unless the labels are also included in an AIM model, then those trajectories will keep their identity.

• Apply the current AIM models

  • 6DOF body not included in the AIM model
    The 6DOF bodies that are separate from the AIM model will not change at all, unless Calculate 6DOF is applied as well.

  • 6DOF body included in the AIM model
    6DOF bodies that are included in the AIM model will be reidentified. However the 6DOF data is not recalculated unless the processing step Calculate 6DOF is activated.