Cross-diffractive optical elements for wide angle geometric camera calibration

Abstract

Diffractive optical elements (DOEs) can generate multiple two-dimensional (2D) diffraction grids that can be used to calibrate cameras for photogrammetry. However, several factors limit the accuracy and the functionality of this technique. One of the most important is the DOE fabrication itself. A large DOE with wide 2D fan-out grids is very difficult and costly to develop. Consequently, the calibration is limited to small aperture cameras and/or limited angles. To overcome these problems, we present a low cost solution. We propose to use two large, commercially available, crossed phase DOEs that generate 15×15 equally spaced dots. As the DOEs are not perfect, the unwanted secondary diffractive orders are used as calibration targets to expand the calibration field of view. We show that the use of the primary and secondary diffractive orders provides a valuable calibration tool for wide angle aerial cameras.

Fisheye lens calibration using virtual grid

“…As discussed in the previous paper [17], the technique will work as long as the entrance pupil of the fisheye can be illuminated by the CDOE (see Fig. 1 and Eq.…”

“…Following the use of two crossed gratings, Thibault et al [17] have shown that the diffractive orders produced by the first grating were not exactly perpendicular to the orders produced by the second grating.…”

“…In order to get a stable, accurate, and compact calibration object, a new setup using cross diffractive optical elements (CDOEs) has recently been proposed and implemented in our laboratory [17]. This idea of calibrating a camera from DOEs was introduced in 2008 by Bauer et al [18].…”

“…We propose a technique that requires the diffractive optical virtual grid to be observed by the camera at a few different orientations to cover the wide FOV of the camera. In our previous work [17], we used the CDOE to calibrate a wide-angle lens that had a 60 deg full FOV using a single image. This work will use a different approach to calibrate a panoramic lens with a 180 deg FOV.…”

Position and orientation measurement adopting camera calibrated by projection geometry of Plücker matrices of three-dimensional lines

“…Camera is an important measurement instrument as it bridges the scales from the 3D space to the 2D space12. Camera calibration is the bridge to estimate the transformation matrix of the camera from a captured photograph3.…”