3D mosaic documentation using close range photogrammetry

The paper describes the close range photogrammetric survey of a roman mosaic stored at Regional Archaeological Museum “Antonino Salinas” in Palermo (Italy). The aim of the work is the production of a full-scale representation (scale 1:1) of the mosaic useful for documentation and restoration processes. The research has allowed evaluating limit and potentiality of image-based approach using photogrammetric and computer vision (Structure for Motion) techniques in a context where the metric point of view is a very important factor

Close-range photogrammetry for accurate deformation distribution measurement

© 2017 Taylor & Francis Group, London. This paper introduces a methodology for improving the accuracy of Deformation Distribution Measurement (DDM) using close-range photogrammetry. After reviewing various algorithms for 2D Digital Image Correlation (DIC), Zero-Normalized Cross-Correlation (ZNCC) is selected for deformation measurement. The impact of several other factors on DIC measurement accuracy has been investigated, including the type of imaging sensors, the contrast and pattern of a specimen, and searching window size. Optimal option of these factors is proposed. The technique is utilized in the experiment of applying static loading on a replica of a concrete structural component used for Sydney Harbour Bridge. Test results presented in the paper include DIC measurements and validation data from conventional sensors

The circular imaging block in close-range photogrammetry

Photogrammetric 3D measuring procedure needs careful planning, especially in the close-range case, in order to fulfill requirements with respect to accuracy and reliability of measurements. In the special case of indoor environment, where imaging is to be taken inside the object space, some difficulties concerning the imaging procedure can be expected. In these environments a special attention has to be paid to the arrangement of sensible imaging geometry, which will guarantee the precision of observations and the reliability of estimates. Sometimes, the division of the measuring task into smaller sub-tasks cannot be avoided. This, however, requires more planning in respect of data registering in order to get the sub-models into the same coordinate system. In this research the issue stated above is studied and a solution to the problems is searched and found via adjusting the imaging procedure suitable to this special case. Great attention is paid to the geometrical aspect of imaging for 3D measurements and robustness of the solution. In this research a new Circular Imaging Block method has been developed for measuring tasks in the inside scene environment. The new method is based on constrained imaging and least squares estimation. One objective of the research has been to simplify the planning stage of the photogrammetric measuring procedure in special circumstances. The controlled imaging procedure improves the opportunity to assess the accuracy of measurements beforehand, and diminishes the need of assistance with an unexperienced user to design and accomplish the imaging. Also, the number of undesirable coordinate transformations can be decreased, since all measurements from one imaging station will be in one and the same coordinate system. Results from real-world experiments verify that an adequate level of accuracy of measurements for object reconstruction in general is attainable with this method. Also, tests indicate that the level of reliability, which is expected in typical close-range measuring cases, can be reached. The advantages of the method can be encapsulated as the straightforwardness of imaging, no need of control data, and the use of assisted automatic procedures in image measurements.reviewe

Discrepancy Analysis Between Close-Range Photogrammetry And Terrestrial LiDAR

This study presents a comparison of building measurements performed on 3D models generated by two different approaches. In one approach, the models were produced via close-range photogrammetry. Such models are based on still-frame photographs that are, post-processed with commercially available photogrammetric software. In the second approach, 3D point-cloud models were generated via laser scanning. For this purpose, three case studies were conducted. The first was a simple one story structure, the second was a multi-story Maya ruin, and the third was an earth filled terrace. Several benchmarks within a closed traverse were established to serve as standard georeference points for all accuracy comparisons. Several physical target points were then marked on the exterior walls of the structure. They are referred here as reference wall points. The reference wall points were then measured with a total-station instrument. After photographs were taken and laser scanning of the structure performed, the coordinates of the reference wall points were also determined from the respective models. The coordinates were then compared with the ones obtained with the total-station instrument. Coordinates and distances from each procedure were compared to determine relative discrepancies and accuracies. The results of this study demonstrate that the close-range photogrammetry can provide accurate enough information to be used as an alternative for total stations or laser scanners when measuring buildings or other relatively small projects

Cultural heritage recording utilising low-cost close-range photogrammetry

Cultural heritage is under a constant threat of damage or even destruction and comprehensive and accurate recording is necessary to attenuate the risk of losing heritage or serve as basis for reconstruction. Cost effective and easy to use methods are required to record cultural heritage, particularly during a world recession, and close-range photogrammetry has proven potential in this area. Off-the-shelf digital cameras can be used to rapidly acquire data at low cost, allowing non-experts to become involved. Exterior orientation of the camera during exposure ideally needs to be established for every image, traditionally requiring known coordinated target points. Establishing these points is time consuming and costly and using targets can be often undesirable on sensitive sites. MEMS-based sensors can assist in overcoming this problem by providing small-size and low-cost means to directly determine exterior orientation for close-range photogrammetry. This paper describes development of an image-based recording system, comprising an off-the-shelf digital SLR camera, a MEMS-based 3D orientation sensor and a GPS antenna. All system components were assembled in a compact and rigid frame that allows calibration of rotational and positional offsets between the components. The project involves collaboration between English Heritage and Loughborough University and the intention is to assess the system’s achievable accuracy and practicability in a heritage recording environment. Tests were conducted at Loughborough University and a case study at St. Catherine’s Oratory on the Isle of Wight, UK. These demonstrate that the data recorded by the system can indeed meet the accuracy requirements for heritage recording at medium accuracy (1-4cm), with either a single or even no control points. As the recording system has been configured with a focus on low-cost and easy-to-use components, it is believed to be suitable for heritage recording by non-specialists. This offers the opportunity for lay people to become more involved in their local heritage, an important aspiration identified by English Heritage. Recently, mobile phones (smartphones) with integrated camera and MEMS-based orientation and positioning sensors have become available. When orientation and position during camera exposure is extracted, these phones establish offthe- shelf systems that can facilitate image-based recording with direct exterior orientation determination. Due to their small size and low-cost they have potential to further enhance the involvement of lay-people in heritage recording. The accuracy currently achievable will be presented also

Relative orientation with limited control in close range Photogrammetry

In close-range photogrammetry, situations can arise in which it is difficult or impossible to establish a network of control points as required for a conventional absolute orientation procedure. The thesis investigates the replacement of the traditional control network by a few control distances measured between well-defined artificial markers or natural feature points. The measured distances must then serve to reduce deformations suffered by the photogrammetric model in the orientation procedures. All investigations are based on analytical rather than analogue photogrammetry. After a review of the concepts of rotation matrices, least squares adjustment and the generation of synthetic image co-ordinate observations, the study is executed in three major steps. A test field of high precision is established by means of space intersection and a camera calibration method for close-range cameras is developed which combines perspective projection with geodetic observations of the lens system parameters. Thus a problem inherent in many camera calibration methods, namely the exact determination of the perspective centre, is largely overcome. Deformation characteristics related to error in elements of interior and relative orientation are determined by the controlled introduction of errors into these elements. The deformations are presented in tabular and diagrammatical form. An analysis of the deformation leads to the conclusions of theoretical and practical relevance for close-range photogrammetry. As a result of the deformation analysis mathematical models are introduced which utilise the measured distances for the reduction of model deformations. The efficiency of homogeneous scaling, affine scaling and convergency correction, as applied individually and in various combinations, is tested. A mathematical formulation of the converging correction as a restraining condition in a least squares adjustment is developed for this purpose. It is shown that a convergency error is less relevant to close-range photogrammetry than generally assumed and that characteristic model deformations in close-range photogrammetry have the character of affine scale errors. Throughout the thesis algorithms are developed which make it possible to execute all computations on computers with limited memory capacity. A program sample for the relative orientation adjustment is given in Appendix IV to demonstrate the memory saving techniques. Finally the results of the investigation are applied to the survey of shoulder height of African elephants in their natural habitat. Equipment and field work are described and results reported

Digital close range photogrammetry in motor vehicle accident reconstruction

Road traffic accidents are consistently in the top ten causes of death world-wide. In order to reduce the number of fatalities caused by traffic collision, better knowledge and understanding of the sequence of events prior to and during a traffic accident, i.e. Accident Reconstruction, is required, so it is important to obtain detailed quantitative information about the damage sustained by the crashed vehicle(s). The research reported here was aimed at developing a fast and accurate method of measuring the damage. Digital Close Range Photogrammetry is the technique chosen for obtaining vehicle profiles from which accurate measurements of crust damage could be made. These profiles can provide valuable information about the collision. They can be used to find the orientation(s) of the vehicle(s) at the moment of impact. The orientation of the vehicle is used to determine the direction of the principal force acting on the vehicle as a function of the relative velocity vector. The depth of the damage sustained can be measured from the profile: this is used to calculate the energy absorbed by the structure from which the pre-impact speed can be calculated. The photogrammetric measuring method is compared with other techniques, for accuracy and speed. A direct comparison is made with the results obtained from Coordinate Measuring Machine and tape measurements. Consideration is given to errors that arise from the reconstruction of three-dimensional space from two dimensional images. The optimal lighting conditions for best results are studied and results are discussed. In addition the repeatability of photogrammetric modelling is evaluated. The technique is applied to vehicles involved in collisions; the photogrammetric models are used to determine the profile of what the vehicles struck and the pre-impact speeds. It is concluded that close range digital photogrammetry is a fast, accurate (12.4mm) and inexpensive (€2000) method of measuring crush damage and hence of considerable benefit in accident investigation

Auxiliary equipment for close range photogrammetry

[ES] Este artículo incluye información del siguiente proyecto de documentación geométrica:● LDGP_mem_012-1: "Documentación geométrica de las excavaciones de la Catedral de Santa María (Vitoria-Gasteiz). Mayo 2000-Junio 2003", http://hdl.handle.net/10810/7212● LDGP_mem_012-1: "Documentación geométrica de las excavaciones de la Catedral de Santa María (Vitoria-Gasteiz). Mayo 2000-Junio 2003", http://hdl.handle.net/10810/7212[EN] This paper includes information from the following project:[ES] Son muchos los artículos técnicos que se pueden encontrar sobre la aplicación de la fotogrametría de objeto cercano a la documentación del patrimonio; sin embargo, un aspecto sobre el que no es habitual encontrar información corresponde a los métodos e instrumentos necesarios para obtener de forma adecuada las fotografías y realizar las tareas topográficas en las dispares circunstancias que el patrimonio requiere. En este artículo se muestra el diseño y utilización de algunos elementos auxiliares utilizados para mejorar la realización de este tipo de pares fotogramétricos.[EN] There are many references where it is described the application of photogrammetric techniques to the documentation of the Cultural Heritage. However, it is not so easy to find texts concerning the auxiliary equipment used in order to get the better conditions for the photographs. In this paper we look over the design and use of some pieces of this kind of equipment