Kyoungmin Lee Il Hong Suh Sang-Rok Oh Wan Kyun Chung Conflict evaluation method for grid maps using sonar sensors. 2908-2914 2008 IROS http://dx.doi.org/10.1109/IROS.2008.4650882 conf/iros/2008 db/conf/iros/iros2008.html#LeeSOC08