Figure 10.

Exploration process: (I) Map established after rounds of exploration; (II) Map after the robot reached point A; (III) Map after the robot reached point B; (IV) Final map after the exploration; Point A is a target point in (I) and a visited topology node in (II–IV); Point B is a target point in (II) and a visited topology node in (III and IV); Point C is a candidate topology node in (I–III) and a visited topology node in (IV); Point O is a visited topology node in (I–IV).