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Dorian Garcia
Abstract
Measurement of 3-D Shapes or 3-D Displacement Fields Using a Stereo-correlation Based Method
Dorian Garcia - 21 december 2001.
Many applications dealing with the mechanical behaviour of materials require the measurement of displacement fields or deformation fields. In order to attain these measurements, optical methods have become unavoidable due to their non-intrusive approach, their high spatial resolution, their high sensitivity, the large size of their examinated field, and the increasing power of the computers that now allow the processing of huge quantities of data.
In this context we have developed a system for measuring 3-D shapes or 3-D displacement fields using a stereo-vision approach (by stereo-correlation).
This method allows: (1) the measurement of the 3-D object shape using a single pair of stereoscopic images of this object and (2) the measure of the 3-D displacement field using at least two pairs of stereoscopic images of an object corresponding to two states of its deformation (or the processing of a sequence of pairs of images acquired during the deformation).
The main topics developed in this thesis are: the strong calibration of a camera or a stereo-vision sensor, the 3-D reconstruction by stereo-vision, the measurement of the 3-D displacement field using a combined stereo-correlation and tracking approach in a sequence of images. Due to the metrology aspect of this research we have paid particular attention to the accuracy of the underlying methods (quality of the calibration, quality of the image matching, subpixel correlation,...).
This work has been succesfully applied to the sheet metal forming (measurement of 3-D shapes and 3-D displacement fields of the stamped parts), to polymer forming (measurement of the 3-D displacement field on a blown elastomere membrane), and to the study of the mechanical behaviour of a refractory ceramic reinforced with metallic fibers (measurement of 3-D displacement fields during a tensile test).
Keywords:
camera calibration, stereovision, correlation based image matching,
non-contacting 3-D metrology, computer vision based experimental mechanics.
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