Working with QTM twin files

The complete data from a QTM twin system measurement is always stored in two separate files. If you have used the Merge with Twin slave option in the processing, the slave file automatically gets the same name as the master with the ending _slave. When the twin slave file is merged with the twin master file, it is then only the 3D data of twin slave that is merged into the file. The twin slave cameras are also displayed as greyed cameras in the 3D view.

The merged twin slave 3D data is marked as Measured slave in the trajectory info windows, but that is the only difference compared with the other data. You can then identify and work with all of the 3D data as usual, for example apply an AIM model to all the data. However if you need to retrack the data you need to do that separately in the twin slave file, since the 2D data is not imported to the master file.

Since only the 3D data is merged from the Twin slave the following processing and input must be performed on the twin master.

• Video (Miqus, Oqus or external video devices)

• Analog data (Analog board or EMG)

• Calculate 6DOF

• Calculate force

• Export data

Merging Twin files in reprocessing

The data of two QTM files can always be merged in reprocessing if you have not been using the Merge with Twin slave option or if you need to redo it because the tracking of the Twin slave file has changed.

The merging is always done by processing the Twin master file and activating the Merge with Twin slave option on the Processing steps list. You can edit both which Twin slave file that is used and the Twin calibration before you reprocess the file. The twin calibration that is used in the reprocessing is shown on the Twin system calibration page. You can change the twin calibration by clicking the Calibrate... button, but you must make sure to click the correct Calibrate button (Manual or Using two measurements) in the Twin system calibration dialog to apply the change, for more information on the Twin calibration settings see chapter Twin System Calibration.

If you use the Reprocess option on the Capture menu to merge the files, then you copy the Twin slave file location either from measurement or project. However you can edit the file location and the Twin calibration on the Twin system page.

If you instead use the Batch process option on the File menu, which file is used is directly controlled by where you copy the settings from.

• processed file
  The Twin slave file and all other Twin system settings are copied from the file that is processed and cannot be changed.

• project and present file
  The processing automatically uses the file with the same name and the _slave extension. However you can edit the Twin calibration if you need to.

Twin 3D data interpolation

It is recommended to use the same frequency in the two systems to avoid any interpolation. If you have to use a lower frequency for the slave system then it is recommended that you use a divisor of the twin master frequency to minimize the interpolation.

The interpolation is a linear interpolation meaning that a line is drawn between the twin slave 3D data. Then any time where the twin slave data does not exist the linear data will be used instead. The interpolated data will have a zero residual so that you can distinguish it in post processing.