IS-1500 User Guide
Thales Visionix, Inc.
MNL- 0024 (D)
Page 35 of 59
4.4.6
Tracker Sigma Data Display
The sigmas represent the degree of uncertainty of orientation and position. A low value is optimal, while high values can indicate poor
tracking. The Tracker Sigma Data display shows the current sigma values and their historical plots.
Note that in the plot shown in Figure 30, the yaw has a higher rotation sigma, and thus a degree of uncertainty, than pitch and roll.
Additionally, the yaw and position sigmas are all steadily increasing as the system continues to use only VINS for tracking. The sudden
drop in sigmas at about 618s occurred when the system had relocalized having viewed the constellation. These occurrences correlate
with what was learned in the Understanding Tracking section about yaw and VINS drift.
Figure 30 – NFT Sigmas Display