Abstract
The accuracy of 3D reconstruction for metrology applications using active stereo pairs depends on the quality of the calibration of the system. Active stereo pairs are generally composed of cameras mounted on tilt/pan mechanisms separated by a constant or variable baseline. This paper presents a calibration approach based on speckle metrology that allows the separation of translation and rotation in the estimation of extrinsic parameters. To achieve speckle-based calibration, a device called an Almost Punctual Speckle Source (APSS) is introduced. Using the APSS, a thorough method for the calibration of extrinsic parameters of stereo pairs is described. Experimental results obtained with a stereo system called the Agile Stereo Pair (ASP) demonstrate that speckle-based calibration achieves better reconstruction performance than methods using standard calibration procedures. Although the experiments were performed with a specific stereo pair, such as the ASP, which is described in the paper, the speckle-based calibration approach using the APSS can be transposed to other stereo setups.
Highlights
The objective of stereovision in the context of metrology is to reconstruct the accurate 3D coordinates of a point P in space using right and left images Pl and Pr of P when observed by cameras situated at different locations
It accepts as inputs: (i) the position of the Almost Punctual Speckle Source (APSS) in the reference frame of the camera found at STEP 1, (ii) the position of the center of gravity of the circles, (iii) R MC found at STEP 3, (iv) initial values for the three elements of TMC, and (v) the values of the angles for the angular positions of the camera
The calibration approach, which was tested on a device called the Agile Stereo Pair (ASP), shows that it achieves better accuracy than standard calibration methods
Summary
The objective of stereovision in the context of metrology is to reconstruct the accurate 3D coordinates of a point P in space using right and left images Pl and Pr of P when observed by cameras situated at different locations. A calibration method based on speckle metrology is presented to uncouple rotation from translation and allows for accurate calibration of extrinsic parameters of active stereo pairs. This device, called the “Agile Stereo Pair” (ASP), shares common features (tilt/pan mechanisms for steering the cameras, adjustable baseline) with many active stereo systems. The approach shares common steps with other approaches published in the literature, it proposes a four-step procedure for the calibration of the transform between the camera reference frame and the reference frame attached to the tilt/pan mechanism This transform, which is key to accurate 3D reconstruction, is ignored by existing techniques. The paper concludes with an overview of the proposed method and proposes future work
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