1,720,983 research outputs found
Marker-free Automatic Matching of Range Data
No full textMatching of multiple views is often addressed in 3D-model generation and is normally a two-stage process consisting of a coarse and a fine matching stage. Coarse matching, that is the pre-alignment of the surfaces for the complex forms, which can be positioned far away from each other in 3D space, is a difficult problem to solve. Fine matching on the other hand can be performed accurately using either the ICP (iterative closest point) method or the least square surface matching method. Nevertheless, ICP involves an iterative solution which consumes much computing time, and it requires models with considerable degree of overlap at the start position. This is because it treats the closest point in the other model as the corresponding point and updates the corresponding relationship in each iterative step. If the models have insufficient overlap, ICP will converge to false result. Consequently, a good coarse matching is a precondition for a successful ICP. The other matching method- least square surface matching- needs a prealigned corresponding relationship between the surfaces of complex objects, exactly the task of the coarse matching process. This paper presents a novel algorithm to perform coarse matching with an innovative data structure, a “matching tree”, which is a combination of a interpretation tree and a bipartite matching graph. The whole systematic process can be divided in three steps: firstly, it performs segmentation of the laser range scan data according to the geometric characteristics; secondly, a coarse matching is conducted to solve the pre-alignment problem; and finally, an efficient fine matching aligns the models accurately. The coarse matching is not affected by the position of the models, because it generated from a matching tree using invariant relationships from the models themselves. This method is particularly suitable for laser range scan point cloud matching of rooms during th
Generalized Procrustes Analysis and its Applications in Photogrammetry Devrim Akca TABLE OF CONTENTS
No full textQuality assessment of 3D building data
Full text linkThis project has been funded by Ordnance Survey Research, the research and development department of the Ordnance Survey of Great Britain, which is gratefully acknowledged. The first author, Devrim Akca, was formerly with the Institute of Geodesy and Photogrammetry of ETH Zurich, Switzerland.Three-dimensional building models are often now produced from lidar and photogrammetric data. The quality control of these models is a relevant issue both from the scientific and practical points of view. This work presents a method for the quality control of such models. The input model (3D building data) is co-registered to the verification data using a 3D surface matching method. The 3D surface matching evaluates the Euclidean distances between the verification and input data-sets. The Euclidean distances give appropriate metrics for the 3D model quality. This metric is independent of the method of data capture. The proposed method can favourably address the reference system accuracy, positional accuracy and completeness. Three practical examples of the method are provided for demonstration.This project has been funded by Ordnance Survey Research, the research and development department of the Ordnance Survey of Great Britain, which is gratefully acknowledged. The first author, Devrim Akca, was formerly with the Institute of Geodesy and Photogrammetry of ETH Zurich, Switzerlanddepartment of the Ordnance Survey of Great BritainPublisher's Versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Akca 1 FULL AUTOMATIC REGISTRATION OF LASER SCANNER POINT CLOUDS
No full textThe registration of point clouds that are acquired from different laser scanner standpoints is an essential task in the environment modelling works. In this paper, a full automatic point cloud registration scheme is presented. Special targets attached onto the object(s) are used as landmarks and their 3-D coordinates are measured with a theodolite in a ground coordinate system before the scanning process. The presented registration scheme can automatically find these targets in the point clouds using radiometric and geometric information (shape, size, and planarity). At the last step, targets are labelled using the consistent labelling by discrete relaxation in order to find the actual names of the points in the ground control points list.
Matching of 3D surfaces and their intensities
No full text3D surface matching would be an ill conditioned problem when the curvature of the object surface is either homogenous or isotropic, e.g. for plane or spherical types of objects. A reliable solution can only be achieved if supplementary information or functional constraints are introduced. In a previous paper, an algorithm for the least squares matching of overlapping 3D surfaces, which were digitized/sampled point by point using a laser scanner device, by the photogrammetric method or other techniques, was proposed [Gruen, A., and Akca, D., 2005. Least squares 3D surface and curve matching. ISPRS Journal of Photogrammetry and Remote Sensing 59 (3), 151–174.]. That method estimates the transformation parameters between two or more fully 3D surfaces, minimizing the Euclidean distances instead of z-differences between the surfaces by least squares. In this paper, an extension to the basic algorithm is given, which can simultaneously match surface geometry and its attribute information, e.g. intensity, colour, temperature, etc. under a combined estimation model. Three experimental results based on terrestrial laser scanner point clouds are presented. The experiments show that the basic algorithm can solve the surface matching problem provided that the object surface has at least the minimal information. If not, the laser scanner derived intensities are used as supplementary information to find a reliable solution. The method derives its mathematical strength from the least squares image matching concept and offers a high level of flexibility for many kinds of 3D surface correspondence problem
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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