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With Nexus 2.1, you can run mixed systems consisting of both Vicon MX T-Series cameras (T10, T20, T40, T160) and Bonita Optical cameras (B3, B10). Nexus gives you access to all the controls and user interface features for both types of camera.
Caution: The use of mixed systems that include Vicon cameras older than T-Series and Bonitas is not supported and is at your own risk.
To obtain optimum performance from a mixed camera system, it is important to understand the difference in strobe power between the larger T-Series cameras and the more compact Bonita models.
❙ Strobe Intensity. All Vicon cameras have a Strobe Intensity control, which is found in the selected camera’s Properties pane, in the Settings section
This control adjusts the intensity of the camera’s strobe independently of the other cameras in the system. Along with other key camera properties such as lens aperture, circle fitting, and sensitivity, Strobe Intensity can be adjusted to create the best set up for data collection in a volume. The Strobe Intensity setting affects the total energy of strobe light produced by a camera. As the voltage supplied to a camera’s LEDs is constant, strobe energy is changed by adjusting the period of time within a strobe ‘on’ cycle to be longer (higher intensity/power) or shorter (lower intensity/power).
❙ Strobe timings. For all current Vicon optical motion capture cameras, the strobe on period (the length of time that the strobe is on) and sensor exposure period (the length of time that the sensor gathers data) are coincident. This means that higher strobe intensities, which have a longer strobe periods, result in longer sensor exposure periods. Lower strobe intensities, which have shorter strobe periods, result in shorter exposure periods. This produces small changes in timing between cameras that have different strobe periods because, despite strobe pulses starting at the same time, they may stop at different times. This results in slight discrepancies in the times of the middle of the pulses.
When you are setting up a mixed camera system, you may need to consider the effect of strobe timings. A single reconstruction is the result of two or more camera sensors recognizing the same marker. If two cameras with significantly different strobe timings are used to capture and reconstruct a marker, small differences in the absolute timing of this data can occur. These differences are generally very small as they will be half of the exposure time difference between two cameras.
Depending on the speed and type of motion being captured, these differences may or may not be a setup consideration. Given other accepted limitations, such as maximum level of calibration accuracy and skin movement artifacts, in a typical setup most of these small differences are insignificant.
When setting up a camera capture system containing both Vicon T-Series and Bonita cameras, it is important to take into account the relative maximum strobe intensity of these cameras. T-Series cameras have a larger, more powerful strobe ring, compared with the smaller Bonita cameras. The Strobe Intensity settings in Nexus are scaled in percent units of the total strobe output. This means that when you slide the value from 0 to 1, a camera’s strobe moves from 0 percent of the strobe’s total power to 100 percent of the strobe’s total power.
The maximum output length of strobe pulse from a Bonita camera strobe is exactly half of the total output of a T-Series camera. To obtain a precise and equal strobe timing and sensor exposure, you must set Strobe Intensity for the T-Series strobe to 50% and for the Bonita strobe to 100%.
In situations where very small timing differences are considered to be relevant and greater than other accepted limitations (such as skin movement artifacts), ensure that all the camera strobe periods match by setting an appropriate value in the Strobe Intensity for the cameras you are using. If all cameras are of the same type, this value is the same for all cameras, but for systems that include both T-series and Bonita cameras, set the Bonita value to half that of the T-Series, as described above. Situations that may warrant this consideration include studies where very fast ballistic movements are expected and/or where very small markers are likely to be in close proximity.
