Using aerial imagery, the JPL FineCalibration (JPL FineCal) software automatically tunes a set of existing CAHVOR camera models for an array of cameras. The software finds matching features in the overlap region between images from adjacent cameras, and uses these features to refine the camera models. It is not necessary to take special imagery of a known target and no surveying is required.
JPL FineCal was developed for use with an aerial, persistent surveillance platform. Synchronized images from an array of cameras are captured and stitched together into a single, very high-resolution image that is projected onto an elevation map of the ground. A GUI (graphical user interface) tool allows the user to play a movie of any part of the imaged surface from any perspective.
JPL FineCal requires, as input, a set of CAHVOR camera models for the camera array. These models are typically developed on the ground using a calibration procedure requiring a known target at a short distance. JPL FineCal corrects the inaccuracy of the camera model extrinsic parameters resulting from the short target distance by using imagery, taken during flight, at an effective distance of infinity. It also makes small improvements to the intrinsic parameters.
JPL FineCal is an automated process that does not require the use of any special targets, and which may be applied during normal flight operations. Thus, it makes it simple to retune the camera models to correct for small misalignments that occur due to changes in aperture settings, vibration, or thermal changes.
This work was done by Daniel Clouse, Curtis Padgett, Adnan Ansar, and Yang Cheng of Caltech for NASA's Jet Propulsion Laboratory.
The software used in this innovation is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-45715.
This Brief includes a Technical Support Package (TSP).
Automated Camera Array Fine Calibration
(reference NPO-45715) is currently available for download from the TSP library.
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Overview
The document outlines the Automated Camera Array Fine Calibration process developed by NASA's Jet Propulsion Laboratory (JPL) to enhance the accuracy of camera models used in aerial imagery. The calibration process is crucial for ensuring precise imaging in various aerospace applications.
The JPLGroundCalibration process serves as the initial step, requiring imagery of known targets collected on the ground. This method optimizes intrinsic camera model parameters, which are essential for accurately projecting light rays through the camera's lens system onto the CCD sensor. However, a significant limitation of this ground-based technique is the proximity of the target, which can lead to inaccuracies in extrinsic parameters—those that define the relative positioning and orientation of the cameras.
To address these inaccuracies, the JPLFineCalibration program utilizes imagery captured during flight, effectively at an infinite distance, to refine the extrinsic parameters while also making minor adjustments to the intrinsic parameters. The process begins with identifying overlapping images and employing a Harris corner detector to find features in the first image. For each detected feature, a corresponding patch is searched in the second image using normalized cross-correlation to determine the best match. This results in a set of matched feature positions, which are then processed to eliminate poor matches through various methods, including homography, affine modeling, and feature consistency checks.
The optimization of camera model parameters is achieved through two runs of the Levenberg-Marquardt algorithm (LMA). The first run focuses solely on optimizing the extrinsic parameters, generating angular and rotational adjustments to minimize discrepancies between paired features. The second run optimizes both extrinsic and intrinsic parameters, resulting in a final, refined camera model.
The document emphasizes the importance of this calibration process in improving the overall accuracy of camera systems used in aerospace missions. It also provides contact information for further inquiries and highlights the proprietary nature of the information, which is subject to U.S. export regulations.
In summary, the JPLFineCalibration program is a sophisticated approach to enhancing camera accuracy in flight imagery, building upon initial ground calibration efforts to ensure high-quality data collection for various scientific and commercial applications.
