Vicon Vantage cameras are purpose-designed motion capture cameras that use multiple high-speed processors to perform real-time proprietary image-processing. When Vicon cameras are set to their normal motion capture mode, they output the movement of Vicon markers, rather than the body to which the markers are attached. This is achieved with the combination of high-powered, narrow-band strobed illumination, retroreflective markers, and a corresponding filter that is tuned to the same wavelength as the strobe. However, to aid setup, Vicon cameras can also be set, one at any one time, to video preview mode. 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). When there is high ambient light, this can aid optimum setup.
Vicon markers are retroreflective spheres that reflect light from the camera strobe units back into the Vicon motion capture cameras. Vicon markers come in a range of sizes that are appropriate for different types of motion capture volumes. The markers are attached to a subject whose motion is to be captured. To obtain accurate results, you must position the markers on the subject at specific anatomical locations. These locations are defined in a Vicon Labeling Skeleton Template (VST) file for a generic type of capture subject or in a calibrated Vicon Labeling Skeleton (VSK) file for a specific capture subject. Your Vicon software documentation describes these files and how you attach markers to your subjects for motion capture in accordance with these files.
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 diagram.
Camera positions will depend on your volume size, camera type, and camera lens. Remember to include height as well as width and depth in your volume calculations.
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 Vantage 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 control in the Vicon application software.
- The accelerometer also determines the orientation of the images in the OLED display.
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 Vantage 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.
To avoid overheating, ensure that the environment in which the cameras are used is well-ventilated.
Vicon Vantage camera performance
Vicon Vantage 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 Vantage 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 Vantage 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 Vantage 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 Vantage 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 Vantage range of cameras, see.