Stability of zoom and fixed lenses used with digital SLR cameras
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Consumer grade digital cameras are widely used for close range photogrammetric applications because of the convenience of digital images and the low cost of capture and reproduction. Since the introduction of digital cameras in the 1980s, there has been a strong divide between relatively inexpensive, low resolution, compact digital cameras, and relatively expensive, high resolution, professional digital cameras. In recent years, the improved affordability of SLR (Single Lens Reflex) style digital cameras has increased the use of this class of camera, to some degree displacing professional cameras. Digital cameras are quite often bundled with a consumer grade zoom lens that is designed for the quality of the image, rather than the geometric stability of the calibration. When these cameras are used for photogrammetric applications, it is common practice that a high quality, fixed focal length lens is purchased and used in preference to the zoom lens. Calibration tests were conducted on a range of different digital cameras, all within the SLR class, to ascertain the differences between zoom and fixed lenses when used with these cameras. Analyses are presented that indicate the differences between the two lens types in terms of accuracy, precision and stability and suggest that although acceptable results can be obtained using zoom lenses, a fixed lens provides superior results.Keywords:
Zoom lens
Digital Photography
Digital camera
Camera lens
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Topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry. Here, we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3D models from field photographs taken with a consumer‐grade camera. The approach integrates structure‐from‐motion (SfM) and multiview‐stereo (MVS) algorithms and, in contrast to traditional photogrammetry techniques, it requires little expertise and few control measurements, and processing is automated. To assess the precision of the results, we compare SfM‐MVS models spanning spatial scales of centimeters (a hand sample) to kilometers (the summit craters of Piton de la Fournaise volcano) with data acquired from laser scanning and formal close‐range photogrammetry. The relative precision ratio achieved by SfM‐MVS (measurement precision: observation distance) is limited by the straightforward camera calibration model used in the software, but generally exceeds 1:1000 (i.e., centimeter‐level precision over measurement distances of 10 s of meters). We apply SfM‐MVS at an intermediate scale, to determine erosion rates along a ∼50‐m‐long coastal cliff. Seven surveys carried out over a year indicate an average retreat rate of 0.70 ± 0.05 m a −1 . Sequential erosion maps (at ∼0.05 m grid resolution) highlight the spatiotemporal variability in the retreat, with semivariogram analysis indicating a correlation between volume loss and length scale. Compared with a laser scanner survey of the same site, SfM‐MVS produced comparable data and reduced data collection time by ∼80%.
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ABSTRACT The production of topographic datasets is of increasing interest and application throughout the geomorphic sciences, and river science is no exception. Consequently, a wide range of topographic measurement methods have evolved. Despite the range of available methods, the production of high resolution, high quality digital elevation models (DEMs) requires a significant investment in personnel time, hardware and/or software. However, image‐based methods such as digital photogrammetry have been decreasing in costs. Developed for the purpose of rapid, inexpensive and easy three‐dimensional surveys of buildings or small objects, the ‘structure from motion’ photogrammetric approach (SfM) is an image‐based method which could deliver a methodological leap if transferred to geomorphic applications, requires little training and is extremely inexpensive. Using an online SfM program, we created high‐resolution digital elevation models of a river environment from ordinary photographs produced from a workflow that takes advantage of free and open source software. This process reconstructs real world scenes from SfM algorithms based on the derived positions of the photographs in three‐dimensional space. The basic product of the SfM process is a point cloud of identifiable features present in the input photographs. This point cloud can be georeferenced from a small number of ground control points collected in the field or from measurements of camera positions at the time of image acquisition. The georeferenced point cloud can then be used to create a variety of digital elevation products. We examine the applicability of SfM in the Pedernales River in Texas (USA), where several hundred images taken from a hand‐held helikite are used to produce DEMs of the fluvial topographic environment. This test shows that SfM and low‐altitude platforms can produce point clouds with point densities comparable with airborne LiDAR, with horizontal and vertical precision in the centimeter range, and with very low capital and labor costs and low expertise levels. Copyright © 2012 John Wiley & Sons, Ltd.
Structure from Motion
Orthophoto
Elevation (ballistics)
Georeference
Digitization
Total station
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Abstract This paper examines the potential of low‐cost digital cameras for close range surface measurement using feature‐based image matching methods. This is achieved through extracting digital elevation models (DEMs) and comparing accuracies between three low‐cost consumer‐grade digital cameras (Sony DSC‐P10, Olympus C3030, Nikon Coolpix 3100) and the proven Kodak DCS460. Surprisingly, the tests revealed that the highest accuracies were achieved using the Sony DSC‐P10, not the Kodak DCS460, whilst the other two cameras certainly proved suitable for most close range surface measurement tasks. Lens modelling was found to provide a limiting constraint on final accuracies, with very small systematic error surfaces caused by residual imperfections in lens modelling. The IMAGINE OrthoBASE Pro software and an independent self‐calibrating bundle adjustment were used to process these data. These tests identified an inaccuracy in the self‐calibrating capability of IMAGINE OrthoBASE Pro version 8·6 and Leica Geosystems LPS 8·7, which will be rectified in subsequent software releases. The study has demonstrated that cheaper consumer‐grade digital cameras have potential for routine surface measurement provided lens modelling is considered. The lead author is maintaining a web‐based repository for camera calibration data, which may assist other users.
Digital camera
Camera lens
Bundle adjustment
Digital Photography
Feature (linguistics)
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Structure from Motion
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Structure from Motion
Bundle adjustment
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Abstract The bundle method is a flexible analytical tool for co‐ordinating engineering and industrial structures. This paper investigates, mainly from a theoretical standpoint, what object space control, if any, need be incorporated in a bundle adjustment and it promotes the use of multistation photography for such projects. The concepts of inner accuracy and free network adjustments are introduced as being valuable in comparative precision studies. Self calibration techniques for the compensation of systematic errors, as well as the detection of gross errors, are also discussed. Résumé La compensation par faisceaux est un outil fort intéressant pour les applications de la photogrammétrie à l'industrie et à l'ingénerie. On recherche ici, en remplaçant surtout d'un point de vue théorique, quelles doivent être alors, s'il en est besoin, les caractéristiques du canevas d'appui. On montre que les concepts d'exacitude interne et de “libre compensation” (équation d'observation indeterminée) présentent un intérêt certain pour ce genre d'étude. On tente également d'évaluer l'intérêt de l'étalouvage et la chambre de prise de vue, et on discute le problème de la détection des fautes. Zusammenfassung Die Bündelmethode ist ein sehr flexibles analytisches Verfahren zur Koordinatenbestimmung beim Ingenieurbau und bei industriellen Konstruktionen. In der Arbeit wird, hauptsächlich vom theoretischen Gesichtspunkt, untersucht, wieviel Objektpasspunkte in einer Bündelausgleichung benötigt werden. Der Autor plädiert für die Anwendung der Multistandpunktaufnahme bei solchen Projekten. Innere Genauigkeit und freie Netzausgleichung werden als wertvolle Begriffe bei vergleichenden Genauigkeitsanalysen angesehen. Die Methoden der Selbstkalibrierung zur Eliminierung systematischer Fehler werden ebenso wie die Verfahren zur Erkennung grober Fehler diskutiert.
Bundle adjustment
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Collinearity
Digital camera
Digital Imaging
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Digital camera
Accuracy and precision
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Abstract We test the acquisition of high‐resolution topographic and terrain data using hand‐held smartphone technology, where the acquired images can be processed using technology freely available to the research community. This is achieved by evaluating the quality of digital terrain models (DTM) of a river bank and an Alpine alluvial fan generated with a fully automated, free‐to‐use, structure‐from‐motion package and a smartphone integrated camera (5 megapixels) with terrestrial laser scanning (TLS) data used to provide a benchmark. To evaluate this approach a 16.2‐megapixel digital camera and an established, commercial, close‐range and semi‐automated software are also employed, and the product of the four combinations of the two types of cameras and software are compared. Results for the river bank survey demonstrate that centimetre‐precision DTMs can be achieved at close range (10 m or less), using a smartphone camera and a fully automated package. Results improve to sub‐centimetre precision with either higher‐resolution images or by applying specific post‐processing techniques to the smartphone DTMs. Application to an entire Alpine alluvial fan system shows the degradation of precision scales linearly with image scale, but that (i) the expected level of precision remains and (ii) difficulties in separating vegetation and sediment cover within the results are similar to those typically found when using other photo‐based techniques and laser scanning systems. Copyright © 2014 John Wiley & Sons, Ltd.
Structure from Motion
Digital camera
Benchmark (surveying)
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