Geometric model and assessment of a dual‐fisheye imaging system

Abstract

This paper presents a technique for the calibration of a 360°dual imaging system (Ricoh Theta S) composed of two cameras with fisheye lenses specially mounted in a common structure. The experiments are based on calibration with a bundle adjustment using the equidistant fisheye lens model and relative orientation stability constraints, such as distance, base elements and rotation matrix between individual cameras' coordinate systems. As a result, an equidistant mathematical model using the Conrady-Brown lens distortion model was shown to be suitable for estimating the interior and relative orientation parameters of the Ricoh Theta S. The main contribution presented in this work is a simultaneous bundle adjustment approach with stability constraints on base elements and rotation matrix angles, which achieved accuracies comparable with conventional photogrammetric calibration with perspective cameras.

A Fisheye Image Matching Method Boosted by Recursive Search Space for Close Range Photogrammetry

“…If the IOPs and ROPs between consecutive images are known, the position of the epipolar lines can be estimated. The IOPs were previously determined in a camera calibration process [21]. As mentioned, the ROP base elements (B X , B Y , and B Z ) and attitude changes (∆ω, ∆φ, and ∆κ) between consecutive images were estimated based on the initial EOPs measured by a navigation system (GNSS/IMU).…”

“…The experimental assessments of the proposed method were performed in a test area located at the São Paulo State University (UNESP) campus of Presidente Prudente, Brazil ( Figure 6). Data sets were acquired using a low-cost personal mobile terrestrial system, known as PMTS [20], which is composed by the poly-dioptric system Ricoh Theta S [21,22] and off-the-shelf navigation systems embedded in a backpack platform ( Figure 5). Figure 5 depicts the PMTS used for a mobile mapping acquisition, aiming a SfM solution.…”

“…A set of 12 images from dataset III was used, which corresponds to 10 m of PMTS trajectory. The bundle adjustment was implemented (C/C++ language) based on the unified approach to the least squares method [26] using the equidistant fisheye lens equations (Ricoh Theta S model) as a mathematical model [21].…”

“…The initial values for the EOPs were applied with standard deviations of 0.5 m for the camera position (X 0 , Y 0 , and Z 0 ) and 10 • for the attitude parameters (ω, φ, and κ). The IOPs were considered as absolute constraints, which were estimated in a previous camera calibration process [21].…”

“…Figure 1 presents a flow chart of the proposed method for recursive feature search (RFS) in fisheye images. The input data include the interior orientation parameters (IOPs) from a previous camera calibration process [21], the initial exterior orientation parameters (EOPs) acquired by a navigation system (global positioning system (GPS) receiver and IMU), and omnidirectional images. The relative orientation parameters (ROP) encompassing the base elements (B X , B Y , and B Z ) and relative rotations (∆ω, ∆φ, and ∆κ) between consecutive images were estimated based on the initial EOPs.…”