Photogrammetric investigation into low-resolution digital camera systems
Digital cameras are becoming the mainstream data acquisition tools in photogrammetry and remote sensing, although not originally and specifically designed for these purposes. In order to fully exploit the technical advances in digital camera and other related technologies, it is necessary to study their metric performances. Usually, a calibration can be carried out to determine and compensate for the systematic errors of camera systems aiming at improving the metric performances of the camera systems. However, no thorough investigation of the metric characteristics of low-resolution digital camera systems has been conducted so far. In addition, the calibration models currently in user were developed for film-based cameras and, thus, cannot properly accommodate certain imperfections of camera systems. This dissertation describes research into the metric performances of low-resolution digital camera systems from both the theoretical and practical aspects. He concepts, working principles, advantages and disadvantages of digital cameras are discussed. The characteristics of an ideal digital imaging device and possible geometric and radiometric error sources of digital camera systems are studied in detail. After a discussion of the current calibration method, a modified calibration model named MFFEM (Multiple-Frame Finite Element Method) is proposed, verified and compared with other models through simulation and a practical case. The metric performances and the accuracy potentials of three typical low-resolution digital camera systems are investigated by conducting a series of well-designed projects. Based on that, the metric applications of such camera systems and the related issues are also touched upon. A software package UNBDCSD (UNB Digital Camera System Calibration) was developed and used for data processing, with the MFFEM function being its main feature. The research findings illustrate that low-resolution digital camera systems can be used for metric purposed with low- or medium accuracy requirements when proper calibration and certain imaging configurations are utilized. The proposed model can compensate for the systematic errors of digital camera systems as effectively as other well-proven models and is advantageous under certain circumstances. Future works lies in the refinement of the software package, combination of geometric and radiometric calibration, and more studies on Finite Element Modeling.