A Flexible, Generic Photogrammetric Approach to Zoom Lens Calibration

Zheng Wang,Zhenhong Li,Rongyong Huang,Wen Xiao,Jon Mills,Shunyi Zheng

doi:10.3390/rs9030244

Zheng Wang, Zhenhong Li + Show 4 more

Open Access

https://doi.org/10.3390/rs9030244

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Abstract

Compared with prime lenses, zoom lenses have inherent advantages in terms of operational flexibility. Zoom lens camera systems have therefore been extensively adopted in computer vision where precise measurement is not the primary objective. However, the variation of intrinsic camera parameters with respect to zoom lens settings poses a series of calibration challenges that have inhibited widespread use in close-range photogrammetry. A flexible zoom lens calibration methodology is therefore proposed in this study, developed with the aim of simplifying the calibration process and promoting practical photogrammetric application. A zoom-dependent camera model that incorporates empirical zoom-related intrinsic parameters into the collinearity condition equations is developed. Coefficients of intrinsic parameters are solved in a single adjustment based on this zoom lens camera model. To validate the approach, experiments on both optical- and digital-zoom lens cameras were conducted using a planar board with evenly distributed circular targets. Zoom lens calibration was performed with images taken at four different zoom settings spread throughout the zoom range of a lens. Photogrammetric accuracies achieved through both mono-focal and multi-focal triangulations were evaluated after calibration. The relative accuracies for mono-focal triangulations ranged from 1: 6300 to 1: 18,400 for the two cameras studied, whereas the multi-focal triangulation accuracies ranged from 1: 11,300 to 1: 16,200. In order to demonstrate the applicability of the approach, calibrated zoom lens imagery was used to render a laser-scanned point cloud of a building façade. Considered alongside experimental results, the successful application demonstrates the feasibility of the proposed calibration method, thereby facilitating the adoption of zoom lens cameras in close range photogrammetry for a wide range of scientific and practical applications.

Highlights

IntroductionIn the case of three-dimensional (3D) reconstruction of cultural heritage sites, photogrammetric approaches have primarily been based on the use of prime lens cameras
To verify the developed approach, zoom lens calibrations for the adopted devices were conducted according to the proposed method
This study has proposed a complete, flexible zoom lens camera model, and presented a comprehensive calibration method based upon this concept

Summary

Introduction

In the case of three-dimensional (3D) reconstruction of cultural heritage sites, photogrammetric approaches have primarily been based on the use of prime lens cameras. The field of view (FOV) of a camera fitted with a prime lens is unchangeable and can be only varied by adjusting the photographer’s location, which can often be restricted by the local environment. Apart from changing focus and aperture settings, a zoom lens camera is capable of adjusting zoom settings to suit different FOV and depths of field (DOF). Zoom lenses have generally been favored in consumer photography and extensively employed for various low accuracy applications in the field of computer vision, e.g., active stereo vision [1], augmented reality [2], and object detection and tracking [3]

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