The combination of the Intersense IS1200 and Airtrack® Precision Rotary Tracking bring a new level of on-stage camera tracking freedom and accuracy. However, to get the most out of the sensor, the tracking reference points on the stage must be set up correctly.
The IS1200 uses a fixed focal length camera with an 80 degree field-of-view to see and recognize binary coded digital optical fiducial targets, as shown here.
This represents fiducial #100. The binary coded digital pattern enables 32,768 different patterns to be recognized, enabling stages of arbitrary size to be successfully tracked.
Using the known positions of the circular fiducial markers, the IS1200 VisTracker is able to calculate its position as long as it sees about 4 markers at all times.
To do this, the Intersense IS1200 first captures a black and white frame through its wide angle lens, and attempts to recognize any fiducial marks that appear in the frame.
The position algorithm will use the quadrilateral formed by the 4 recognized targets that are furthest from the center of the lens to solve for the 3D position of the camera. In this case, the 4 furthest targets would be **100, 250, 1000, and 850.**
The further toward the edges that the recognized targets appear, and the more accurately their absolute 3D coordinates are known, the more accurate the solve.
Acquisition and Tracking Modes
The IS1200 VisTracker actually has two operating modes. The IS1200 starts up automatically in acquisition mode then automatically moves to tracking mode.
The VisTracker is always in one of these modes. The IS1200 toggles between these modes automatically.
In acquisition mode, the VisTracker is looking at the constellation file it has loaded an it tries to identify fiducial markers in its field-of-view.
By marking an area for where targets are visible and identifiable, the IS1200 can then calculate its position.
Acquisition time depends on the size of the constellation file and the distance to the fiducial markers. On average, acquisition time should be no longer than 25-30 seconds at the most.
When using upwards of 300 fiducial markers, or 60 five-marker boards, acquisition can take up to 60-80 seconds, depending on the height of the targets.
In tracking mode (or tracquisition mode), the IS1200 is constantly detecting fiducial markers and measuring its position in relation to the markers.
In this mode, the IS1200 VisTracker is much more robust and is able to detect markers that may not be initially detectable during acquisition.
In tracking mode, the VisTracker is also operating in a “predictive tracking” mode. This means that even if a fiducial target is not perfectly exposed or not completely in focus, as long as it’s not occluded, if it’s in the field-of-view of the VisTracker, the marker is being used to track.
In Optical Data Display Tool, “predictive tracking” is visible through white bounding boxes: whenever the VisTracker sees anything circular in a position it expects, it places a bounding box around it. If this circle is both in an expected position and the fiducial marker is legible, then it also gets a small green cross.