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Qualisys System

The Qualisys Motion Capture System is a high-precision motion capture system that is installed in the CRS lab at Technopark (PFA). It is used to provide high-quality pose and twist estimates for tracks, environment objects and agents.

Documentation index — full table of contents.

Qualisys Track Manager (QTM)

The Qualisys Track Manager (QTM) is the desktop application employed to manage the camera setup (calibration). Its reference manual and an overview are available on the Qualisys product page.

A machine running QTM on Windows 10 is set up in the lab and assigned a static IP address on the local network.

Launching QTM

todo

Creating and Modifying Objects in QTM

Creating Objects in QTM

An object is created in the 3D preview pane by selecting the markers belonging and creating it.

  1. Switch to the 3D view.
  2. Find all the markers attached to an object. Hold ctrl and click on all markers belonging to an object (or hold shift and drag an area around them). The markers should turn white when clicked.
  3. Right-click after selecting all markers and choose Define rigid body (6DOF).
  4. Enter a name for the object. This name will also set the published frame name in ROS.
  5. Note that the origin of the object is set at the centroid of its markers, which may not coincide with the center of mass. If necessary, move the origin.

Qualisys Bridge

We use a third-party library by KTH-SML to connect to the QTM application Windows 10 machine. The third-party library registers with QTM and opens a port on the local machine where pose / twist data is received.

We have then the following data flow:

QTM --> mocap_library --> /tf --> /namespace/tf_republisher_node --> /mocap/topic_name/

In particular, to bridge the TransformStamped messages published on /tf (where all frames are published under the same topic) by the library, we have a republishing node that listens to transforms on /tf for a particular frame and then republishes under a topic that the estimator can subscribe to.

Configuration

The Qualisys system is configured using the Qualisys Track Manager (QTM) software. The software is installed on a Windows 10 machine in the lab.

Moving the Origin

By default, the coordinate origin of any new object is placed as the centroid of the markers placed on the object. This is not ideal in many cases, as for example the track marker's centroid does not coincide with the origin.

To move the origin of an object, follow these steps:

  1. Open the Settings window by clicking the gear icon in the top left corner.
  2. Choose 6DOF Tracking in the left sidebar.
  3. Select the object whose origin you want to move.
  4. Click the Translate button in the Origin section.
  5. Choose So that point in the body has local coordinates (in mm) as an option, and enter the known coordinates of the desired marker in the text fields.