Great question.
The positions are continuously updated based on the estimated error of the measurement, as well as the error estimate of the current position estimate of the marker.The position error estimate is based on the estimated error of previous measurements, and the errors on the other markers that are visible at the same time.
I believe that this approach is similar to many graph SLAM methods, except we are not currently doing any global error minimization at the moment.
We would like to add bundle adjustment, or a similar global optimization system to both improve the mapping and even adjust the camera calibration to reduce the error in measurement, but we haven’t been able to put the time necessary into it yet. (We do accept PRs if you want to add this 
)
Rohan
Ubiquity Robotics
ubiquityrobotics.com