Abstract
Abstract. A novel calibration process of RICOH-THETA, full-view fisheye camera, is proposed which has numerous applications as a low cost sensor in different disciplines such as photogrammetry, robotic and machine vision and so on. Ricoh Company developed this camera in 2014 that consists of two lenses and is able to capture the whole surrounding environment in one shot. In this research, each lens is calibrated separately and interior/relative orientation parameters (IOPs and ROPs) of the camera are determined on the basis of designed calibration network on the central and side images captured by the aforementioned lenses. Accordingly, designed calibration network is considered as a free distortion grid and applied to the measured control points in the image space as correction terms by means of bilinear interpolation. By performing corresponding corrections, image coordinates are transformed to the unit sphere as an intermediate space between object space and image space in the form of spherical coordinates. Afterwards, IOPs and EOPs of each lens are determined separately through statistical bundle adjustment procedure based on collinearity condition equations. Subsequently, ROPs of two lenses is computed from both EOPs. Our experiments show that by applying 3*3 free distortion grid, image measurements residuals diminish from 1.5 to 0.25 degrees on aforementioned unit sphere.
Highlights
According to the representation of the field of view (FOV), cameras are classified into two main groups: classical cameras with narrow FOV and omnidirectional cameras with very large FOV
Schneider et al (2009) developed four geometric models for fisheye lenses based upon stereographic, equidistance, equisolid and orthogonal projection geometry to project object points to images and they added additional parameters to calibrate the images that are captured from a 14 Megapixel camera equipped with Nikkon 8 mm fisheye lens
Calibration is performed for nine networks on image; we have ten ∆φ and ten ∆λ in unit sphere as Interior orientation parameters (IOPs)
Summary
According to the representation of the field of view (FOV), cameras are classified into two main groups: classical cameras with narrow FOV and omnidirectional cameras with very large FOV. Rays are straight lines and intersect in the projection centre, but fisheye images are defined based on specific projection equations as follows: (Kannala and Brandt, 2006; Schneider et al, 2009). Schneider et al (2009) developed four geometric models for fisheye lenses based upon stereographic, equidistance, equisolid and orthogonal projection geometry to project object points to images and they added additional parameters to calibrate the images that are captured from a 14 Megapixel camera equipped with Nikkon 8 mm fisheye lens.
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