Photogrammetric technique for in-flight ranging of trailing vortices using entrained balloons

A method for experimentally determining the radial distance of a probe aircraft from a trailing vortex is described. The method relies on photogrammetric triangulation of targets entrained in the vortex core. The theory and preliminary testing were described using laboratory mock-ups. Solid state video cameras were to provide data at 300 Hz rates. Practical methods for seeding the vortex are under separate investigation and are not addressed

Fisheye Photogrammetry to Survey Narrow Spaces in Architecture and a Hypogea Environment

Nowadays, the increasing computation power of commercial grade processors has actively led to a vast spreading of image-based reconstruction software as well as its application in different disciplines. As a result, new frontiers regarding the use of photogrammetry in a vast range of investigation activities are being explored. This paper investigates the implementation of fisheye lenses in non-classical survey activities along with the related problematics. Fisheye lenses are outstanding because of their large field of view. This characteristic alone can be a game changer in reducing the amount of data required, thus speeding up the photogrammetric process when needed. Although they come at a cost, field of view (FOV), speed and manoeuvrability are key to the success of those optics as shown by two of the presented case studies: the survey of a very narrow spiral staircase located in the Duomo di Milano and the survey of a very narrow hypogea structure in Rome. A third case study, which deals with low-cost sensors, shows the metric evaluation of a commercial spherical camera equipped with fisheye lenses

Airborne LiDAR for DEM generation: some critical issues

Airborne LiDAR is one of the most effective and reliable means of terrain data collection. Using LiDAR data for DEM generation is becoming a standard practice in spatial related areas. However, the effective processing of the raw LiDAR data and the generation of an efficient and high-quality DEM remain big challenges. This paper reviews the recent advances of airborne LiDAR systems and the use of LiDAR data for DEM generation, with special focus on LiDAR data filters, interpolation methods, DEM resolution, and LiDAR data reduction. Separating LiDAR points into ground and non-ground is the most critical and difficult step for DEM generation from LiDAR data. Commonly used and most recently developed LiDAR filtering methods are presented. Interpolation methods and choices of suitable interpolator and DEM resolution for LiDAR DEM generation are discussed in detail. In order to reduce the data redundancy and increase the efficiency in terms of storage and manipulation, LiDAR data reduction is required in the process of DEM generation. Feature specific elements such as breaklines contribute significantly to DEM quality. Therefore, data reduction should be conducted in such a way that critical elements are kept while less important elements are removed. Given the highdensity characteristic of LiDAR data, breaklines can be directly extracted from LiDAR data. Extraction of breaklines and integration of the breaklines into DEM generation are presented

A new method to determine multi-angular reflectance factor from lightweight multispectral cameras with sky sensor in a target-less workflow applicable to UAV

A new physically based method to estimate hemispheric-directional reflectance factor (HDRF) from lightweight multispectral cameras that have a downwelling irradiance sensor is presented. It combines radiometry with photogrammetric computer vision to derive geometrically and radiometrically accurate data purely from the images, without requiring reflectance targets or any other additional information apart from the imagery. The sky sensor orientation is initially computed using photogrammetric computer vision and revised with a non-linear regression comprising radiometric and photogrammetry-derived information. It works for both clear sky and overcast conditions. A ground-based test acquisition of a Spectralon target observed from different viewing directions and with different sun positions using a typical multispectral sensor configuration for clear sky and overcast showed that both the overall value and the directionality of the reflectance factor as reported in the literature were well retrieved. An RMSE of 3% for clear sky and up to 5% for overcast sky was observed

Reliability in Constrained Gauss-Markov Models: An Analytical and Differential Approach with Applications in Photogrammetry

This report was prepared by Jackson Cothren, a graduate research associate in the Department of Civil and Environmental Engineering and Geodetic Science at the Ohio State University, under the supervision of Professor Burkhard Schaffrin.This report was also submitted to the Graduate School of the Ohio State University as a dissertation in partial fulfillment of the requirements for the Ph.D. degree.Reliability analysis explains the contribution of each observation in an estimation model to the overall redundancy of the model, taking into account the geometry of the network as well as the precision of the observations themselves. It is principally used to design networks resistant to outliers in the observations by making the outliers more detectible using standard statistical tests.It has been studied extensively, and principally, in Gauss- Markov models. We show how the same analysis may be extended to various constrained Gauss-Markov models and present preliminary work for its use in unconstrained Gauss-Helmert models. In particular, we analyze the prominent reliability matrix of the constrained model to separate the contribution of the constraints to the redundancy of the observations from the observations themselves. In addition, we make extensive use of matrix differential calculus to find the Jacobian of the reliability matrix with respect to the parameters that define the network through both the original design and constraint matrices. The resulting Jacobian matrix reveals the sensitivity of reliability matrix elements highlighting weak areas in the network where changes in observations may result in unreliable observations. We apply the analytical framework to photogrammetric networks in which exterior orientation parameters are directly observed by GPS/INS systems. Tie-point observations provide some redundancy and even a few collinear tie-point and tie-point distance constraints improve the reliability of these direct observations by as much as 33%. Using the same theory we compare networks in which tie-points are observed on multiple images (n-fold points) and tie-points are observed in photo pairs only (two-fold points). Apparently, the use of two-fold tiepoints does not significantly degrade the reliability of the direct exterior observation observations. Coplanarity constraints added to the common two-fold points do not add significantly to the reliability of the direct exterior orientation observations. The differential calculus results may also be used to provide a new measure of redundancy number stability in networks. We show that a typical photogrammetric network with n-fold tie-points was less stable with respect to at least some tie-point movement than an equivalent network with n-fold tie-points decomposed into many two-fold tie-points

Determining the parameters of cylinders using digital photogrammetry for application to pipe measurement in industrial plants

Bibliography: p.187-193.The maintenance and expansion of piping systems of petro-chemical plants is a complex and costly process. These costs can be reduced by knowledge of the as-built dimensions and layout of the piping system. As-built Computer Aided Design (CAD) models of such piping systems, specifically the use of Plant Design System (PDS) software packages, allow for more efficient planning than paper plans. Conventional surveying and analogue photogrammetry have been methods that have traditionally been used to capture the necessary CAD information. More recently, the Department of Geomatics at the University of Cape Town has produced software which replicates the analogue photogrammetric approach using digital images (Cammidge, 1996). The objective of this thesis is to develop a pipe measurement technique which can supplement those currently being used and overcome some of their shortcomings. A further objective is to present an overview of the pipe measurement techniques, photogrammetric principles, image processing techniques and programming considerations which would be required to develop a robust, fully functional, pipe measurement software package integrated with a PDS. The author hopes that this thesis will form the foundation for the development of such a software package for local and possibly international industry. A digital photogrammetric technique related to line photogrammetry is developed. This technique makes use of lines in an image which represent the silhouette edges of the cylinder. The use of photogrammetry based on lines avoids some of the shortcomings of conventional point-based photogrammetry. It is not necessary to identify conjugate points in images, nor is it even necessary for overlapping images of the cylinder to be captured. Furthermore, this thesis reports on a number of tests designed to gauge the developed techniques' accuracy and suitability for use in pipe metrology in an industrial plant. The techniques were found to be capable of achieving results which deviated by, on average, 2-3mm in object position and 0.1° in direction from the likely true values of the cylinder axis. The radius could be determined to better than 1 mm. The techniques developed here proved to be suitably accurate for the purpose of determining the parameters of pipes in industrial plants. However, certain factors may reduce the accuracy and these are also discussed. This thesis concludes that a novel digital photogrammetric technique for measuring pipes in an industrial plant was successfully developed. Recommendations are made as to how the technique might be improved to allow sub-millimetre accuracies to be obtained. Finally, a recommendation is made that the information contained within the thesis be used as the basis for designing a digital photogrammetric measurement module to be linked to a PDS

3D Computational Ghost Imaging

Computational ghost imaging retrieves the spatial information of a scene using a single pixel detector. By projecting a series of known random patterns and measuring the back reflected intensity for each one, it is possible to reconstruct a 2D image of the scene. In this work we overcome previous limitations of computational ghost imaging and capture the 3D spatial form of an object by using several single pixel detectors in different locations. From each detector we derive a 2D image of the object that appears to be illuminated from a different direction, using only a single digital projector as illumination. Comparing the shading of the images allows the surface gradient and hence the 3D form of the object to be reconstructed. We compare our result to that obtained from a stereo- photogrammetric system utilizing multiple high resolution cameras. Our low cost approach is compatible with consumer applications and can readily be extended to non-visible wavebands.Comment: 13pages, 4figure

The design of a digital photogrammetric metrology system for the semi-automated surveying and recording of pipe dimensions in industrial plants

Bibliography: pages 51-53.This thesis reports on the design, development and testing of a semi-automated system to aid in the mapping of the interior of industrial plants. The system makes use of digital photogrammetry to assist an operator in locating and identifying components of the plants. All of the important photogrammetric theory is discussed in the text, and explained in detail in the appendices. Specifically, this system implements various algorithms used for camera calibration, object point intersection, and a method combining the two techniques. Considerable use is made of the iterative least squares method, which is the basis of many of the algorithms employed in this work. Image processing algorithms are implemented to enhance the digital images, and to ease the identification of objects in the images, and these are fully explained in the text. Adaptive least squares image matching is a method of matching corresponding points in different images and is used to ensure correspondence between points identified by the system operator. A weighted centre of gravity method is used to find the centre of target areas, and an algorithm is implemented to determine the radius, centre and direction of a pipe passing through a number of points. Various aspects of the system design are discussed and explained. In particular the requirements in terms of hardware and software are presented. In addition, the choices of the operating system and of the compiler are justified. Potential problems with the system, and possible enhancements of it are also described. Tests were performed to verify the correct operation of all of the algorithms used in the calibration of the cameras. Together with the point intersection routines, these tests calculated the position of various control points, the correct coordinates of which were previously known. The calculated point positions are compared to the known coordinates of the points to determine the accuracy of the various algorithms. Further tests were conducted to demonstrate and verify the ability of the system to measure distance in three dimensions. These tests illustrate that the accuracy achievable is approximately 0.053 of the total distance measured for an object occupying 803 of the width of the image. The system improves considerably on the method presently used in South Africa and in many industries worldwide which rely on analytical photogrammetry for the determination of object point locations. While the system suffers from reduced accuracy as a result of the use of digital cameras, this problem will become less important as technology and digital camera resolution improve. Possible enhancements include the use of more numerically efficient algorithms, and the introduction of techniques that would partially automate the identification of control points and pipes

Optimal Camera Placement to measure Distances Conservativly Regarding Static and Dynamic Obstacles

In modern production facilities industrial robots and humans are supposed to interact sharing a common working area. In order to avoid collisions, the distances between objects need to be measured conservatively which can be done by a camera network. To estimate the acquired distance, unmodelled objects, e.g., an interacting human, need to be modelled and distinguished from premodelled objects like workbenches or robots by image processing such as the background subtraction method. The quality of such an approach massively depends on the settings of the camera network, that is the positions and orientations of the individual cameras. Of particular interest in this context is the minimization of the error of the distance using the objects modelled by the background subtraction method instead of the real objects. Here, we show how this minimization can be formulated as an abstract optimization problem. Moreover, we state various aspects on the implementation as well as reasons for the selection of a suitable optimization method, analyze the complexity of the proposed method and present a basic version used for extensive experiments.Comment: 9 pages, 10 figure