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Performance Analysis and Validation of a Stereo Vision System

This paper presents an in-depth performance analysis and validation of a correlation based stereo vision system being used as part of the ongoing 2003 Mars Exploration Rover flight mission. Our analysis includes the effects of correlation window size, pyramidal image down-sampling, vertical misalignment, focus, maximum disparity, stereo baseline, and range ripples. A key element of validation is to determine the stereo localization error both analytically and experimentally. We study both down-range and cross-range error and verify that while camera calibration inaccuracy contributes to both, stereo correlation error affects only the former. Error contributions of subpixel interpolation, vertical misalignment, and foreshortening on stereo correlation are examined carefully. A novel method using bricks with reflective metrology targets and a mast-mounted stereo camera system enabled experimental measurements of the stereo disparity error. The standard deviation of the down-range disparity error was measured at sigma=0.32 pixel for high-resolution 1024times768 camera images. The result is critical in evaluating accurate rover navigation and instrument placement within given error budgets