A portable 3-D shape measurement system based on the combined stereovision and phase shifting method

A portable 3-D shape measurement system based on a combined stereovision and phase shifting method which can realize big scale objects measurement is proposed. This system uses two pre-calibrated cameras and one projector which do not need to be calibrated. During the whole measurement procedure, the projector is used to project a visibilitymodulated fringe pattern on the object and is relatively fixed to the object. The two cameras are set up for stereovision and grab fringe images simultaneously. The cameras can be moved to as many positions as needed to capture single views and these single views can then be transformed into the same global coordinate system to reconstruct the whole 3- D model. Since the phase value at each pixel is used to assist stereo matching only, it does not have to be accurate and the errors caused by inaccurate phase measurement, for example, periodic errors due to the nonlinearity of the projector's gamma curve are eliminated. These two high frame rate cameras can grab images as fast as 180 fps. Using the visibility-modulated fringe pattern the phase information in one direction and fringe visibility information in the other direction can be obtained simultaneously for stereo matching. Therefore only three images are needed for a single view, which means the image acquisition time for each view is just 13.9ms. Experimental results are presented to show the feasibility of this method.