1,720,999 research outputs found
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Higher-dimensional modelling of geographic information
No full textOur world is three-dimensional and complex, continuously changing over time and appearing different at different scales. Yet, when we model it in a computer using Geographic Information Systems (GIS), we mostly use 2D representations, which essentially consist of linked points, lines and polygons. These representations are relatively easy to use and efficient, and a wide variety of methods is built on top of them. However, 2D representations are necessarily limiting. They force us to reduce problems to two dimensions, limit the type of objects we can represent, and complicate storing the relationships between different objects—especially when these are across time and different scales. Nevertheless, most research in GIS is devoted to improving these 2D representations, as well as to the development of new methods that build on them to solve problems, both old and new. This thesis explores a new, fundamentally different modelling approach—integrating both spatial and non-spatial characteristics as dimensions in the geometric sense, specifically targeting the cases of time and scale. While this has been proposed before at a conceptual level, this thesis aims to realise the fundamental aspects of a higher-dimensional GIS by developing higher-dimensional (nD) representations, as well as new methods operating on them to create, manipulate and visualise geographic information. As this thesis shows, the higher-dimensional approach is undoubtedly memory-intensive, but it is also very powerful, as it provides a simple and consistent way to store geometry, attributes and the topological relationships between objects of any dimension. This generic approach can also be easily extended to handle other non-spatial characteristics, enabling better data management that is consistent across dimensions and more powerful operations, such as checking if two objects are adjacent at any point in time. In order to model higher-dimensional space, it is best to consider an nD space subdivision as a base, which is conceptualised as an n-dimensional simplicial complex or cell complex. This can then be implemented with a simplex-based data structure, with an incidence graph, as a set of Nef polyhedra, or—as done in this thesis—by using ordered topological models such as the cell-tuple and generalised/combinatorial maps. Creating computer representations of higher-dimensional objects can be complex. Common construction methods used in 2D and 3D, such as directly manipulating combinatorial primitives, or using primitive-level construction operations (such as Euler operators), rely on our intuition of 2D/3D geometry, and thus do not work well in higher dimensions. It is therefore all too easy to create invalid objects, which then cannot be easily interpreted or fixed—a problem that is already exceedingly apparent in three dimensions. As a way to easily create representations of higher-dimensional objects, this thesis proposes three novel higher-level methods, all of which are intuitive to use and attempt to create valid output. Extrusion takes an (n-1)-dimensional cell complex and a set of intervals per cell, projecting them parallel to a new axis in order to create an n-dimensional cell complex. Incremental construction describes an n-dimensional object based on its (n-1)-dimensional boundary, from dimension zero (points) and then upwards. Finally, a 4D model can be constructed from a series of 3D models at different levels of detail (LODs) by linking them. In order to visualise higher-dimensional models, as well as to be able to process them in existing software, it is important to have methods to extract meaningful 2D/3D subsets from them. % Such methods would consist of two steps: (i) selecting a subset of the objects in the model and (ii) projecting this subset to a lower dimension. As a stepping stone towards such methods, this thesis shows how n-dimensional to (n-1)-dimensional orthographic and perspective projections can be defined. Finally, this thesis placed an emphasis on validating the algorithms with real-world datasets, which was only possible by developing methods to repair the invalid datasets that are widespread in practice. This thesis thus contains methods to create valid polygons and planar partitions using a constrained triangulation of the input, as well as a method to repair polyhedra and space subdivisions by snapping together lower-dimensional primitives and removing overlaps using Boolean set operations on Nef polyhedra. This allowed tests with up to 6D datasets based on real-world data—a good base for higher-dimensional GIS. In the future, the work in this thesis will be extended with higher-dimensional modification operations, true 4D spatiotemporal datasets and repair methods with quality guarantees. All implementations made for this thesis are publicly available under open source licences.UrbanismArchitecture and The Built Environmen
A Voronoi- and surface-based approach for the automatic generation of depth-contours for hydrographic charts
No full textDepth-contours are an essential part of any hydrographic chart—a map of a waterbody intended for safe ship navigation. Traditionally these were manually drawn by skilled hydrographers from a limited set of surveyed depth measurements. Nowadays this process of map making is shifted towards the digital domain, not in the last place because of the huge amounts of data resulting from modern surveying techniques. Furthermore, the task of automating the process of cartographic generalization that depends on subjective criteria is challenging. The produced depth-contours should comply with the four hydrographic generalization constraints of safety, legibility (smoothness), topology and waterbody morphology. I show that grid-based approaches to generalize depth contours that are currently used in practice do not always comply with those fundamental generalization constraints. Most notably, the safety constraint, that ensures that a map never indicates an area as being shallower than measured, is often violated. But also the legibility and morphology constraints are not always optimally respected. Furthermore, heterogeneous datasets (that contain a transition of very sparse to very dense data), can lead to unwished interpolation artifacts, when the popular Inverse Distance Weighting (IDW) spatial interpolation method is used. Part of this problem is the non-adaptive nature of IDW, that requires the user to re-set the interpolation parameters when the spatial distribution of the input point changes. I present and prototype a novel surface-based approach for the generalization of hydrographic depth-contours that is based on the Voronoi Diagram (VD) and performs generalization on the surface that defines the contours, rather on the contour lines individually. Through the VD, a fully adaptive, automatic and smooth spatial interpolation method known as the Laplace interpolant is coupled with a Delaunay Triangulation (DT) data structure that contains all data points with their exact planimetric coordinates. Using this concept a number of operators is defined that are able to perform the relevant cartographic generalization operations for hydrographic contours: simplification, smoothing, aggregation, omission and enlargement. The significance of the proposed approach lies herein that it honors all four hydrographic generalization constraints, most notably: it is guaranteed to be safe. As opposed to current automated approaches, it does therefore not require any form of manual safety verification. And, because all of the employed algorithms are local, it is also well scalable to big datasets in principle.GeomaticsGIS technologyOTB Research Institute for the Built Environmen
Knowledge-based optimisation of three-dimensional city models for car navigation devices
No full textThree-dimensional maps are deemed better for navigation purposes as they offer a larger number and more realistic navigation cues than two-dimensional maps. Improvements in two key technologies have opened the doors towards utilization of 3D maps for car navigation devices. Advances in data acquisition technologies and data processing methods have made creating photorealistic three-dimensional city models cheaper and to a large extent automatic, while advances in mobile technologies have made e.g. modern smartphones powerful enough to visualize photorealistic 3D graphics. Despite the latter improvements, making three-dimensional mobile maps remains a challenge due to the large amounts of data and the device’s limited amount of memory and pro- cessing power. These limitations can be overcome by intelligently reducing the amount of information that is handled and displayed by the device. This thesis presents an information reduction and prototyping framework that reduces the amount of information contained in city models so a to enable their loading and display on car navigation devices. The information reduction method consists of two steps. The first step selects buildings that are close to the driver’s route with the idea that these aid the driver in navigating. Buildings that are far from the route are discarded. In the second step, the selected buildings’ external representation is adapted to match their navigational value that is based on their thematic, semantic and cognitive properties. For instance, a building of type ’restaurant’ and ’brand’ McDonald’s offers more navigational cues than a block of gray, anonymous residential buildings. The latter are styled in generic textures whereas the former is styled in photorealistic textures. The relations between a building’s semantic and thematic properties and its external representation are captured in visualisation rules. A prototype is built that implements the designed information reduction methods and tests their effectivity. The selection step is performed using a spatial database while the visualisation rules are processed by an expert system. The reduced 3D scenes are displayed in a game engine that also performs performance measurements. The obtained results are conclusive: the performance of a visualisaion in terms of frame rate and used graphics memory is governed by the the amount of textures, much more so than the number of geometries. Effort should therefore be directed towards the reduction and/or simplification of textures rather than geometries.GeomaticsGIS technologyOTB Research Institute for the Built Environmen
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Storage and analysis of massive TINs in a DBMS
No full textAdvances in technologies to collect elevation data are far superior to the advances to store and process the resulting point clouds. This paper investigates the use of a DBMS to store and manage not only the points coming from massive point-based datasets, but also a TIN of these points. TINs are used as a support structure to implement processing and manipulation operators. I discuss in the paper why storing efficiently a TIN in a DBMS is a complex task, and I propose a new solution. It does not store explicitly triangles, as only the star of each point is stored. The details of the data structure are discussed and compared with other solutions currently available.OTB OnderzoekOTB Research Institute for the Built Environmen
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