Vicon Valkyrie cameras in a Valkyrie system

Vicon Valkyrie cameras are purpose-designed motion capture cameras that use multiple high-speed processors to perform real-time proprietary image-processing. When Vicon cameras are in their normal motion capture mode, they output the movement of Vicon markers, rather than the subject to which the markers are attached. (To use the cameras in Video Preview mode, which is useful when you are setting up the cameras in the volume, see Vicon Valkyrie Video Preview mode). This is achieved with the combination of high-powered, narrow-band strobed illumination, retroreflective or active markers (which contain infrared active LEDs that are visible to the Vicon cameras), and a corresponding filter that is tuned to the same wavelength as the strobe.

Vicon markers can be retroreflective spheres that reflect light from the camera strobe units back into the Vicon motion capture cameras, or active markers, which contain infrared LEDs that are visible to the Vicon cameras. The markers are attached to a subject or object whose motion is to be captured. For information on the file types involved in Vicon motion capture and on how to position markers on your subjects in accordance with these files, see your Vicon application software documentation.

You position the cameras around the capture volume to ensure full coverage of the subjects whose motion you will be capturing. Data from at least two cameras is required to produce 3D reconstructions of the Vicon markers, so ensure that the placement and orientation of all cameras results in multiple cameras aimed at the same region of the capture volume, as shown in this image. For help in visualizing your volume camera coverage, try the Vicon Visualization Tool on the Vicon website.

Camera positions will depend on your volume size, camera type, and camera lens. 

Depending on your capture requirements, you may choose to mount the cameras on tripods for floor-based cameras or on a clamp and truss on speed rails for raised cameras.

For more information, see also:

Vicon Valkyrie Video Preview mode

To help with setting up the cameras in a volume for positioning, focus, and field of view, you can set Valkyrie cameras, one at any one time, to Video Preview mode (for instructions, see the Vicon Valkyrie Quick Start Guide or the documentation for your Vicon application software).

Video Preview mode outputs a lower resolution image of the whole scene at approximately 30 fps (the exact rate is the closest multiple of the system frame period). It works best where there is good ambient light.

When the system frame rate is greater than the maximum frame rate achievable at full resolution (see Vicon Valkyrie technical specifications for the maximum frame rate for each camera variant), to enable you to see the same view as the camera in optical mode, the camera uses windowing to display the image. For this reason, we recommend that, while setting up your Valkyrie system, you reduce the system frame rate below the maximum. When you have finished setting up the system, increase the frame rate to its required setting.

Vicon Valkyrie accelerometer

Each camera is fitted with an accelerometer which has several purposes:

• Before the system is calibrated, you can tap the camera to alert the Vicon application software that you are setting up that particular camera. The software then responds accordingly.
• After the system has been calibrated, if the camera is accidentally knocked or bumped, an alert is sent to the Vicon application software so that you can take the appropriate action. You can change how hard the camera has to be knocked to cause it to report a bump by altering the Bump Detection Sensitivity or Bump Sensitivity control in the Vicon application software.
• The accelerometer also determines the orientation of the images in the Valkyrie display on the front of the camera.

Note the following limitations of bump detection:

• Bump detection is active only on calibrated cameras.
• Bump detection cannot detect movement that does not change the gravity vector, for example. slow translation with no rotation.
• Bump detection cannot detect movements that occur when the camera is not connected to a live system.
• The camera is detected as bumped when the reading from the accelerometer is sufficiently different from the last reading. Gradual changes (for example, a slipping camera mount) may not be detected until there is enough of a change to trigger a new notification.

Vicon Valkyrie temperature sensors

Electronic temperature sensors in the camera body and strobe relay information back to the Vicon application software. This lets the user of the software know when the system has stabilized and that the system is ready for calibrating. If a problem occurs due to overheating, which is caused by too high an ambient temperature, the Vicon application software can inform the user of a potential problem.

You can change the required temperature range in the Vicon application software.

Vicon Valkyrie camera performance

Vicon Valkyrie cameras evaluate an entire image in grayscale, rather than applying a black and white threshold. This provides more information and increases motion measurement accuracy over an equivalent resolution black and white camera. The Vicon Valkyrie cameras perform the majority of data processing. They generate grayscale blobs from the retro-reflective markers in the capture volume and then use centroid-fitting algorithms to determine their accurate centers, or collate the whole grayscale data if the markers are deemed to be merged. This camera data is sent to the Vicon application software for further processing and viewing. For details, see your Vicon software documentation.

A number of factors affect the overall performance of your Valkyrie system. These include camera resolution, number of cameras, capture rate, and number of markers/subjects captured. All of these factors impact the overall data rate of your system and may affect the specification required for your Vicon Valkyrie host PC. Understanding the expected data rate can also help to inform you whether a standard single Gigabit Ethernet connection is sufficient or whether a configuration that involves link aggregation may be preferable.

You can specify the required frame rate in your Vicon application software on the Vicon Valkyrie host PC. Your Vicon application software remembers this setting and re-applies it on power up or from reset. You can also configure the buffering of camera data at the time of capture. For details, see your Vicon software documentation.

For a comparison of the performance of the models in the Vicon Valkyrie range of cameras, see Vicon Valkyrie camera performance comparison.