Page 179 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 11

A
Initial Position Estimate A''
U U yAz
Az

UxAz

Implied Position and Azimuth
for Full Correction

Figure 11.11. Apparent position uncertainty as a result of azimuth uncertainty

Figure 11.11 demonstrates how we might determine the error in the apparent posi-
tion of the column that could be contributed by azimuth uncertainty. We simply take
the vector from the robot’s current position estimate to the compensated measured
position A″ and rotate it by the azimuth uncertainty (U ). The x and y position dif-
Az
ferences between the two vectors’ ends (U and U ) are the possible x and y errors
xAz
yAz
that could be attributable to the azimuth being incorrect.
Unfortunately, this observational uncertainty may add to or subtract from the appa-
rent position error caused by the robot’s lateral and longitudinal uncertainty (its true
position error). However, we can estimate the likelihood that an observed error was
the result of the vehicle’s position error vs. its heading error. We will call these factors
the observational quality for the lateral and longitudinal corrections.

162