## LIDAR Navigation Basics

A ring of 8 LIDAR sensors has been added to the ISR Mini Explorer so that its navigation capabilities could be improved. The sensors are spaced 45 degrees from each other so that all the 360 degrees could be covered by a sensor. Each one of the LIDAR sensors can measure absolute distances from 5 centimetres up to 2 meters with 1 milimeter resolution, low deviation and have a field of view of 25 degrees.

A decomposition of the map in 5 by 5 centimetres cells has been made. Coordinate transformations of all the cells to every sensor were calculated to find which of the cells belongs to each sensor's field of view. Then, using the Thrun solution combined with the inverse model of the sensor, the map was calculated.

The navigation algorithm used was the Virtual Force Field algorithm [1] in which two virtual forces are calculated. The attractive force is only influenced by the destination point and its distance to the current robot coordinates. The repulsive force is influenced by all the cells in the map. The cells with higher probability of occupation contribute more to this repulsive force than the ones with lower probability. In the end, both the attractive and repulsive forces are added and the resultant vector guides the robot to its destination point.

[1] J. Borenstein and Y. Koren, "Real-time obstacle avoidance for fast mobile robots," in IEEE Transactions on Systems, Man, and Cybernetics, vol. 19, no. 5, pp. 1179-1187, Sept.-Oct. 1989