S-PIV comparative assessment: image dewarping plus misalignment correction and pinhole plus geometric back projection

This study describes the comparative analysis of two stereoscopic particle image velocimetry (S-PIV) techniques. Emphasis is given to the accuracy of the calibration procedure. Both techniques are related to the angular displacement concept. The first method is based on the pinhole model and is taken as a reference. The second method is based on two steps: the cross-correlation of a calibration pattern to obtain the image's dewarping function; and the cross-correlation of experimental images to evaluate and correct for the misalignment between the calibration and measurement planes. The methods' accuracy is compared on the basis of experimental data from a translation-rotation stage, which allows to simulate uniform displacements and misalignments in terms of offset and rotation. The simulation shows that the measurement accuracy is highly sensitive to relative misalignment between the target and measurement planes. A misalignment correction procedure taking into account the residual disparity between the dewarped images is proposed, compensating for most of the error with an overall less sensitive method to the misalignment.