Optimal calibration of a prism-based videoendoscopic system for precise 3D measurements

Modern videoendoscopes are capable of performing precise three-dimensional (3D) measurements of hard-to-reach elements. An attachable prism-based stereo adapter allows one to register images from two different viewpoints using a single sensor and apply stereoscopic methods. The key condition for achieving high measurement accuracy is the optimal choice of a mathematical model for calibration and 3D reconstruction procedures. In this paper, the conventional pinhole camera models with polynomial distortion approximation were analyzed and compared to the ray tracing model based on the vector form of Snell’s law. We, first, conducted a series of experiments using an industrial videoendoscope and utilized the criteria based on the measurement error of a segment length to evaluate the mathematical models considered. The experimental results confirmed a theoretical conclusion that the ray tracing model outperforms the pinhole models in a wide range of working distances. The results may be useful for the development of new stereoscopic measurement tools and algorithms for remote visual inspection in industrial and medical applications.The Russian Science Foundation (project #7-19-01355) financially supported the work. The authors thank A. Naumov, A. Shurygin and D. Khokhlov for continuous technical support

Reconstruction of three-dimensional surface structure of hard-to-reach objects using prism-based stereoscopic systems

Video endoscopes with stereoscopic prism-based optical systems are widely used for non-destructive testing and geometric measurements of hard-to-reach elements inside complex technical objects. The functionality of the existing devices of this type is limited to a great extent by the capabilities of the embedded software. In this paper, we present our software for the calibration of such systems and the processing of obtained stereoscopic images. It allows to reconstruct and process the whole array of three-dimensional coordinates of the observable object points, to compare it with the reference surfaces and to export the data to other mathematical software.The reported study was funded by RFBR according to the research project № 17-29-03469

Calibration simulation for stereoscopic optical systems using optical design software

To reconstruct three-dimensional (3D) structure of objects and measure their geometric parameters using stereoscopic imaging systems, it is necessary to implement a number of image processing algorithms. For higher system efficiency, the choice of these algorithms and mathematical models should be taken into account at the stage of optical system design. We demonstrate the capabilities of optical design software to perform computer simulation of geometrical calibration for stereoscopic systems. The simulation allows comparison of mathematical models used for 3D reconstruction and estimation of 3D measurements errors caused by tolerances of optical elements, temperature variations and other factors. Using this technique, we analyze the design of prism-based stereoscopic system and show that the proposed ray tracing camera model considering pupil aberrations provides higher measurement precision. The results of computer simulation are confirmed by experiments with the self-developed stereoscopic system