Camera Calibration from a Single Imaged Ellipsoid: A Moon Calibration Algorithm

TL;DR

This paper presents a novel method for calibrating spacecraft cameras using images of moons and planets modeled as ellipsoids, achieving high accuracy from a single image and improving with multiple images.

Contribution

It introduces the first camera calibration technique that works from a single non-spherical ellipsoid image, applicable to both space and terrestrial cameras.

Findings

Achieves <1 mm accuracy in focal length estimation from a single image.

Reduces uncertainty with multiple images, reaching 0.5 mm in focal length.

Successfully applied to Cassini spacecraft images of Saturn's moons.

Abstract

This work introduces a method that applies images of the extended bodies in the solar system to spacecraft camera calibration. The extended bodies consist of planets and moons that are well-modeled by triaxial ellipsoids. When imaged, the triaxial ellipsoid projects to a conic section which is generally an ellipse. This work combines the imaged ellipse with information on the observer's target-relative state to achieve camera calibration from a single imaged ellipsoid. As such, this work is the first to accomplish camera calibration from a single, non-spherical imaged ellipsoid. The camera calibration algorithm is applied to synthetic images of ellipsoids as well as planetary images of Saturn's moons as captured by the Cassini spacecraft. From a single image, the algorithm estimates the focal length and principal point of Cassini's Narrow Angle Camera within 1.0 mm and 10 pixels, respectively. With multiple images, the one standard deviation uncertainty in focal length and principal point estimates reduce to 0.5 mm and 3.1 pixels, respectively. Though created for spacecraft camera calibration in mind, this work also generalizes to terrestrial camera calibration using any number of imaged ellipsoids.