FöRFATTARE
Mascarenhas, Canute

INSTITUTION
Rymdvetenskap, Kiruna /

SAMMANFATTNING
The planetary rovers must be able to accurately, quickly, and reliably perceive the terrain for navigation. The main objective of the thesis is to realize a laser-based optical system for obstacle detection at unknown terrain for a planetary rover. The optical system consists of an active light emitter that projects a pattern of laser beams onto terrain surface, and a CMOS camera captures images and the image processing software identifies the variations in the pattern as it encounters differen obstacles. The proposed Active Light system is deployed on a MERLIN rover. The approach based on active light is expected to offer substantially reduced sensing costs, allowing more reliable navigation through unstructured areas. The implemented purely vision based algorithms rely on capturing and detecting deformation in the laser pattern. Simple straight forward Template matching method and Boundary masking method are proposed initially. Subsequently optical flow [28] based and CamShift [29] based obstacle detection methods are implemented to overcome the limitations posed by earlier methods. The real world environment is highly unstructured and dynamic, each of the four algorithms, for obstacle detection, have certain advantages and limitations. The dynamics in the captured image due to rover motion is unpredictable, since it is governed by an unknown number of parameters. Obstacle detection becomes a more complicated problem in outdoor scenes, where numerous factors are controlling the scene in a very unpredictable way. A Meanshift [30] based approach is used for estimating pattern shifts in video sequence due to rover vibrations. Active Light sensor reliably recognizes obstacles irrespective of their shape in real- time. The performance of the system is evaluated on wide variety of terrains, for each of the image processing based obstacle detection methods. The results of the experiments demonstrate that the proposes system using CamShift based method is more accurate and efficient compared with other methods, enabling the rover to navigate safely

ISSN 1653-0187 / ISRN LTU-PB-EX--08/031--SE / NR 2008:031