Qualisys
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 Screenshot of Qualisys QTM version 2024.2 | |||||||||
| Website | www.qualisys.com | ||||||||
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Qualisys is a Swedish manufacturer of high-end optical motion capture systems. Several Qualisys systems are in use within the Faculty of Social Sciences.
Motion capture data can be collected and processed using QTM, for which a site license is available.
Cameras
A Qualisys system is an optical motion capture system, meaning it uses cameras to record motion of your subject. This is traditionally done with markers, which emit or reflect infrared light that can be captured by the cameras. By placing multiple cameras in different locations, the system can triangulate the position of a marker.
A typical capture setup (in our labs) consists of 8-10 cameras, placed in a circle around the capture area. Usually, all cameras in a system are the same type, but Qualisys cameras can be mixed and matched to some extent. Cameras with the same connector can be daisy-chained together, and otherwise separate "loops" can be joined via a network switch. When combining different cameras, the maximum frame rate of the entire system is limited to the maximum frame rate of the "worst" camera.
Every Qualisys camera can be used in either "Marker mode" or "Video mode". In Marker mode, they contribute to calculating the 3D position of each marker. In Video mode, the camera captures a regular video (avi), to either aid in labeling markers and movements, or to process for markerless motion capture. Cameras in Video mode do not contribute to marker tracking.
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| Oqus 5 | Miqus Hybrid | |
| Resolution | 2048 x 2048 (4MP) | 1920 x 1088 (2 MP) |
| Field of View [fn 1] | 49° | 61° x 37° |
| Connector | Lemo | PoE |
| Marker Mode | ||
| Max. Range [fn 2] | 25m | 13m |
| Max. Frame Rate [fn 3] | 180-10.000 fps | 340 fps |
| Video Mode | ||
| Color | Infrared (b&w) | Full color |
| Max. Frame Rate [fn 3] | 25 fps | 85-550 fps |
Markers
Passive markers are little (hemi)spheres covered in retro-reflective material. They reflect the light emitted by the cameras, so that they show up on the camera's sensor. Markers come in all sizes from 2 - 50mm, and with different atachment methods (glue-on, velcro or screw). Choice of marker size depends on the subject and the distance between the subject and the cameras. The smaller the subject (e.g. baby's fingers), the smaller the marker needs to be. But the smaller the marker, the higher the resolution or the closer the camera should be to capture it.
The benefit of using passive markers is that they are (relatively) cheap, and they need no cables for power or anything. The downside is that passive markers are not inherently identifiable, meaning they need to be manually labeled afterwards and cannot be streamed in real-time unless they are part of a rigid body. A rigid body is an object with 3 or more markers
All optical markers (both active and passive) have the disadvantage of being easily obscured (something blocking the view from the cameras to the marker, making it impossible to track). Therefore, marker placement has to be considered carefully, and often it is wise to place additional markers for redundancy. Standard marker placement templates exist for full/partial body tracking.
Active Markers
Active markers are markers that emit infrared light themselves. They require an active power source (meaning they're attached to cables), but they can potentially work over longer distances, and most of all they can be individually identified.
The TSG is currently testing Qualisys' "Traqr" active marker systems; they will likely be available for use in the labs in the near future.
Usage
If you wish to capture motion with a Qualisys system, please contact the TSG. They will assist you in determining which system is best suited for your needs and, when available, will set it up for you in one of our research labs. A training session with Erik van den Berge is required before you can use the system.
LSL
Data from QTM can be streamed in real-time via LSL using the Qualisys LSL App. Only labeled markers (3D) and rigid bodies (6DOF) can be streamed over LSL.
Data Processing
When you have captured marker data, you can process it in QTM to label the markers and fill any gaps. Some analysis tools are available within QTM; otherwise you can export the data in a suitable format (c3d, matlab, tsv, fbx). You can request access to QTM on your own PC from Erik van den Berge.