A probabilistic map is created on the basis https://github.com/UbiquityRobotics/fiducials. However instead of formulating a SLAM problem, the pose of a master marker is estimated based on observation of many markers.
This package implements a system that uses ceiling mounted fiducial markers (think QR Codes) to allow a robot to identify its location and orientation. It does this by constructing a map of the ceiling fiducials. The position of one fiducial needs to be specified, then a map of the fiducials is built up from observing pairs of markers in the same image. Once the map has been constructed, the robot can identify its location by locating itself relative to one or more ceiling fiducials.
Documentation is at http://wiki.ros.org/fiducials.
Sometimes for trobleshooting purposes it is useful to record a bag file to capture the exact data on the topics going into and out of fiducials.
To do this, while the system is running, run rosbag record -a.
You can upload this bag file to a file sharing service like Google
Drive and link to it in your issue, this will help us diagnose
the problem.