What does frontier mean?
In an occupancy grid, a free cell with at least one unknown neighbour: a place the robot can reach that borders space it has not yet seen. Exploring means driving to frontiers until none are left.
In a lesson
That is the whole idea, from Yamauchi in 1997, and it has survived because it is exactly right. A frontier is a place the robot can reach, since it is free, that borders on something it has not seen. Driving to a frontier is guaranteed to produce new information. When there are no frontiers left and the robot can reach everywhere, the map is finished, and the robot knows it is finished, which is a surprisingly hard property to get any other way.
Learn it
- Taught in U8.6 Frontiers Mapping, University