Examination of the Influence of Lens Distortion of Non-Metric Digital Cameras on the Accuracy of Photogrammetric Survey

U radu se ispituje utjecaj radijalne i tangencijalne distorzije objektiva nemjernih digitalnih kamera na točnost fotogrametrijske izmjere, i to prije svega metodom računanja fototriangulacije sa samokalibracijom. Kao testno polje za određivanje distorzije upotrebljava se 2D-predložak s oznakama mjerenima metodom slikovnih korelacija. Prikazani su rezultati koji upućuju na presudan utjecaj radijalne i tangencijalne distorzije na rezultate fotogrametrijske izmjere, ali i samokalibracije. Stoga se predlaže neovisno prethodno određivanje utjecaja distorzije i njezina eliminacija prije samokalibracije. Rezultati su potvrđeni neovisnim izjednačenjem fototriangulacije s novouvedenim parametrima.This paper examines the influence of radial and tangential lens distortion of non-metric digital cameras on the accuracy of the photogrammetric survey, primarily using the method of photo-triangulation with self-calibration. 2D-template with the marks measured using image correlation is being used as a test field to determine the distortion. The results indicate decisive influence of radial and tangential distortion on the results of photogrammetric measurements and also of self-calibration. Therefore, we propose an independent predetermination of the effects of distortion and its elimination before self-calibration. The results were confirmed by independent equalization of photo-triangulation with newly introduced parameters

An Online Self-calibrating Refractive Camera Model with Application to Underwater Odometry

This work presents a camera model for refractive media such as water and its application in underwater visual-inertial odometry. The model is self-calibrating in real-time and is free of known correspondences or calibration targets. It is separable as a distortion model (dependent on refractive index $n$ and radial pixel coordinate) and a virtual pinhole model (as a function of $n$). We derive the self-calibration formulation leveraging epipolar constraints to estimate the refractive index and subsequently correct for distortion. Through experimental studies using an underwater robot integrating cameras and inertial sensing, the model is validated regarding the accurate estimation of the refractive index and its benefits for robust odometry estimation in an extended envelope of conditions. Lastly, we show the transition between media and the estimation of the varying refractive index online, thus allowing computer vision tasks across refractive media.Comment: 7 pages, 6 figures, Submitted to the IEEE International Conference on Robotics and Automation, 202

Camera distortion self-calibration using the plumb-line constraint and minimal Hough entropy

In this paper we present a simple and robust method for self-correction of camera distortion using single images of scenes which contain straight lines. Since the most common distortion can be modelled as radial distortion, we illustrate the method using the Harris radial distortion model, but the method is applicable to any distortion model. The method is based on transforming the edgels of the distorted image to a 1-D angular Hough space, and optimizing the distortion correction parameters which minimize the entropy of the corresponding normalized histogram. Properly corrected imagery will have fewer curved lines, and therefore less spread in Hough space. Since the method does not rely on any image structure beyond the existence of edgels sharing some common orientations and does not use edge fitting, it is applicable to a wide variety of image types. For instance, it can be applied equally well to images of texture with weak but dominant orientations, or images with strong vanishing points. Finally, the method is performed on both synthetic and real data revealing that it is particularly robust to noise.Comment: 9 pages, 5 figures Corrected errors in equation 1

Blind Detection and Compensation of Camera Lens Geometric Distortions

This paper presents a blind detection and compensation technique for camera lens geometric distortions. The lens distortion introduces higher-order correlations in the frequency domain and in turn it can be detected using higher-order spectral analysis tools without assuming any specific calibration target. The existing blind lens distortion removal method only considered a single-coefficient radial distortion model. In this paper, two coefficients are considered to model approximately the geometric distortion. All the models considered have analytical closed-form inverse formulae.Comment: 6 pages, 4 figures, 2 table

In-flight calibration of the Apollo 14 500 mm Hasselblad camera

In-flight calibration of 500-mm Hasselblad camera flown on Apollo 1