Photogrammetric system of non-central refractive camera based on two-view 3D reconstruction

Due to the harsh construction environment of tunnels, the visual system must be fitted with a sphere cover of a certain thickness. The visual system with an optical sphere cover invalidates conventional measurement methods. Therefore, this paper provides a comprehensive visual measurement method using spherical glass refraction. First, the spherical glass refraction imaging is modeled using a geometry-driven camera model. Second, a three-parameter calibration method for the optical center offset unit vector, incident optical path offset distance, and optical center offset distance was proposed to accurately characterize refractive distortion. Then, a dynamic interval (DI) based on angle and depth constraints is introduced, and a DI-SGM algorithm utilizing the semi-global stereo matching method is developed to solve the polar constraint failure problem under refraction. Finally, an improved binocular parallax method that uses refraction image pairs is proposed and demonstrated to be effective and stable under spherical refraction using effectiveness and comprehensive data experiments. The constructed DI has narrow characteristics. The imaging model presented in this paper has an average space reconstruction error of only 0.087 mm. The maximum measurement error for sphere center distance is only 0.157 mm, which is comparable in accuracy to the case with no refraction. The proposed method provides an effective approach for applying visual measurement methods under refractive effects, thereby improving the visual system’s reliability in tunnel environments.