Camera review: Part 2 - Qualisys

Part 2 in our camera review series. Click below to read our posts on other systems:

Sony RXOii

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Another excellent hardware partner with Theia is Qualisys, who have a synchronized video camera solution that is compatible with Theia3D.

Components: A typical system would consist of 8 cameras, a switch, power adapters, and a high bandwidth NIC connected to a desktop computer.

Setup: Of all the cameras we support, this is the only system where the cameras are daisy-chained together. What this means is that the cameras are connected to each other, so they don’t need to all connect back to the switch. This reduces the total length of cords by quite a bit, simplifying setup. Every third trio of cameras requires a power adapter, which also transfers the data back to the PC. So, for the 8 camera system, you would need three power adaptors, which transfer data back to the switch, which is then connected to the computer.

Data recording and transfer: Qualisys has a software product called Qualisys Track Manager (QTM) that records videos from the Miqus high speed cameras. This handles the synchronization of the cameras, and records the data directly to the computer. So, data collection is as simple as clicking start and stop, and the videos are stored directly on the PC.

Calibration: Another interesting feature about these cameras is that they also have the ability to record infrared data, and they take advantage of this for their calibration process. To calibrate, you place an l-frame with infrared markers in the volume, and wave the wand around (these products are provided by Qualisys). This has all the advantages and disadvantages of infrared calibration, which is available elsewhere (very accurate, some potential difficulties with glare). Furthermore, the lenses are calibrated in-house by their technicians, so, while they don’t have varying focal lengths, the lens parameters provided are very accurate, and you don’t need to do this step once you have the cameras. Importantly, the output file that QTM saves can be loaded directly into Theia3D, so there is no need to modify anything between the calibration and markerless analysis.

Benefits: The integration within QTM is excellent. In addition to being able to record videos and calibration in isolation, QTM can also run automated analysis through their PAF applications. For baseball, running, and gait, getting from data collection to a report requires clicking only a few buttons. They have fully integrated their automated workflows into Theia3D and the results are impressive.

Setting up the cameras and calibrating is also very simple. We are fortunate enough to have a few of these systems, and moving them around and resetting them up has never been an issue. Moreover, their track record of integrating systems will make you feel confident that you always have synchronous data when collecting with multiple modalities, such as with a force plate, and that the data will be in the same global reference frame.

The interface is easy to navigate, and allows flexibility in camera settings, resolutions, and capture rates, without making them overly complicated.

Need to know: The only real consideration is image windowing at higher frame rates. Due to data throughput limitations, the full 1080P collections can only be done at 85 FPS, so to collect faster motions, the sensor needs to be windowed. So, for faster motions, you need to be careful with camera placement, because a smaller part of the video sensor is being used.

Overall, the integration provided by Qualisys is an excellent option for labs that have existing hardware that require integrations. Furthermore, almost all of the third party validation has been done with this system, so you have a good idea as to what you can expect from the system in terms of accuracy!

Do you have more questions? Click here to learn more about using Theia3D with a Qualisys system.