1,721,016 research outputs found
Photometric stereo for 3D mapping of carvings and relieves: case studies on prehistorical art in Sardinia
No full textA photogrammetric technique (Photometric Stereo), known since a long time, is here proposed as an agile an cheap tool for 3D recording engravings and relieves. Different from stereoscopic or monoscopic Photogrammetry, the Photometric Stereo uses a standard camera at a fixed point to take typically four snapshots of the same object under different lighting directions. Image processing gives three maps: the “Albedo” (that is the color of the surface without any shading), the x-gradient and the y-gradient. From gradient maps one gets the 3D shape of the original surface, with results comparable with those obtained by the much more expensive and demanding laser scanning machines. The 3D surface, once re-colored with the original Albedo, renders highly natural virtual reconstructions. The key point is the extreme simplicity of the acquisition procedure and the preservation of the 3D information even under non-ideal conditions. Examples will be given on decorations of the sadinian “Domus de Janas”
Tecniche di modellazione 3D per una documentazione accurata delle incisioni rupestri: confronto tra Structure from Motion e Photometric Stereo
No full text3D modelling represents a fundamental survey technique to represent archaeological
evidence. It is particularly important to draw and analyse engravings because it is more descriptive
and, somehow, objective than traditional drawings, which result interpretative and
not replicable, becoming a debatable and often controversial matter. A technique able to verify
the overlaying of signs is essential to establish the relative sequence, thus the chronology of
engravings. However, the techniques are more than one and give different results. The paper
tries to empirically compare SfM and PS methods to understand how they work surface representation
and what are their specificities in a difficult context such as the Pianaùra engravings.
The aim of the paper is to verify the accuracy of the techniques. Three paths are pursued: the
first applies analyses of pure quantitative data, such as counting the number of points or faces
built and so on; the second aims to verify quantitatively distortions by geometric measurements
analysis; the third is a visual quality test, which focuses on users’ perception of 3D models.
It can be concluded that the different fields of application and the different purposes of the
research enhance the different specificities of the two techniques
Recent improvements in photometric stereo for rock art 3D imaging
No full textRecent improvements in photometric stereo (PS) are shown to remove the major limitations of this low-cost 3D recording technique. In particular, there are significant improvements in lighting constraints, processing time and presence of deformation in reconstructed surfaces, allowing for fast and accurate restoration of shape and color information. The shooting technique is sufficiently easy to make PS ideal for ancient rock art, which is generally encountered in difficult to access sites, where many of the rock engravings to survey are often placed in a narrow space. This paper focuses on the Sardinia neolithic tombs known as Domus de Janas, as the offer an opportunity to demonstrate the applicability of PS to general rock ar
Nuovi sviluppi nelle tecniche di stereofotometria 3D di incisioni e rilievi. Applicazioni nella tomba XV di Sos Furrighesos, Sardegna
No full textHere is proposed a Photogrammetric technique known since a long time as Photometric Stereo, as cheap and easy technique for taking 3Ds of rock art engraving and relieves. Unlike stereoscopic or monoscopic photogrammetry, this technique uses a standard reflex camera fixed in the same point of view for each shot, under different lighting direction. The image processing gives back three images: the x and y gradients and the “albedo”, which is the surface real color without any shading
interference. The 3D surface is recreated from the gradient maps, with good results comparables with the ones taken from the laser scanner, and a very natural appaearance thanks to the Albedo recovery color. The exceptional acquisition aptitude and preservation of the 3D information even under non-ideal conditions and arduous locations is the crux of this technique This presentation is focused on the considerables improvements recently achieved in application modes, execution times and quality results. As example, here are presented the results in XV grave of the Sos Furrighesos’ necropolis in Sardinia
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
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
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