IS-1500 User Guide
Thales Visionix, Inc.
MNL- 0024 (D)
Page 19 of 59
2.2.3
PRA Fiducial Tracking
InterSense optical inertial trackers such as the IS-1500 are capable of tracking off of fiducials like the
ones found on the poster included with the hardware kit. InterSense fiducials are circular black-and-
white patterns that act as known physical landmarks for the system. A fiducial constellation refers
to the layout of all fiducials in a tracked area. When placed on a flat, level surface, the poster serves
as the default fiducial constellation for the IS-1500 system. Constellations and their fiducials provide
predetermined points of reference for the tracker. Fiducial constellations enable another level of
drift correction and set a fixed environment reference frame for the system.
The circular patterns of the fiducials are key to their functionality. The three circles within the pattern
(the center eye and two outer eyes) are what the system’s image recognition component uses to
recognize a pattern as a fiducial. These circles also serve as the tracked points. Damage to any of
these three points, especially the center eye, can render a fiducial unidentifiable to the system.
Because the InertiaCam is a visible light tracker reading black-and-white fiducials, uneven lighting
across the constellation can also render the fiducials unidentifiable during pattern recognition.
The rest of the pattern acts like a barcode. The black and white sections are decoded by the software
and translated to a numeric value. The numerical value is known as the fiducial ID. In a single
constellation, no two fiducials can share a fiducial ID. They must all have a unique ID and therefore a unique pattern. Figure 14
shows the constellation as seen in the Optical Data display. The fiducial overlays shows a square around each recognized fiducial with
crosshairs for each eye. The numbers indicate the fiducial IDs.
Figure 14 – Fiducial Overlay
Figure 13 – Default
Fiducial Constellation