IDENTIFYING A POSITION OF A MARKER IN AN ENVIRONMENT

A technique is described herein for determining the position of at least one previously-placed physical marker in a physical environment. In one approach, the technique detects the marker at plural vantage points in the environment, to yield plural instances of marker information. The technique then computes the position of the marker based on the plural instances of marker information collected at the plural vantage points. The technique may also provide a movement indicator that assists the user in moving to specified vantage points in the physical environment. The technique may use the identified position(s) of the marker(s) to accurately place virtual objects relative to real-world objects in a modified-reality world.