1,721,001 research outputs found
Hyper-hemispheric lens distortion model for 3D-imaging SPAD-Array-based applications
No full textPanoramic omnidirectional lenses have the typical draw-back effect to obscure the frontal view, producing the classic donut-shape image in the focal plane. We realized a panoramic lens in which the frontal field is make available to be imaged in the focal plane together with the panoramic field, producing a FoV of 360° in azimuth and 270° in elevation; it have then the capabilities of a fish eye plus those of a panoramic lens: we call it hyper-hemispheric lens. We built and test an all-spherical hyper-hemispheric lens. The all-spherical configuration suffer for the typical issues of all ultra wide angle lenses: There is a large distortion at high view angles. The fundamental origin of the optical problems resides on the fact that chief rays angles on the object side are not preserved passing through the optics preceding the aperture stop (fore-optics). This effect produce an image distortion on the focal plane, with the focal length changing along the elevation angles. Moreover, the entrance pupil is shifting at large angle, where the paraxial approximation is not more valid, and tracing the rays appropriately require some effort to the optical designer. It has to be noted here as the distortion is not a source-point-Aberrations: it is present also in well corrected optical lenses. Image distortion may be partially corrected using aspheric surface. We describe here how we correct it for our original hyper-hemispheric lens by designing an aspheric surface within the optical train and optimized for a Single Photon Avalanche Diode (SPAD) array-based imaging applications. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only
Depth Calibrations of a 2D-CMOS-Based Partially Coherent Light Interferometer
No full textThis work concerns the development of a 3D measuring system able to realize noncontact surface topography with millimetric depth-range and micrometric resolutions both in the spatial and depth axes. The optical concept is based on the well known low coherence interferometry (LCI) technique. The most widespread set-up of such technique is that of measuring only a point at a time with a 2D scanning system that permits the measure on an area. The novel concept of our instrument is based on the use of a 2D sensor (CMOS), where every single pixel measures a point on the object and this permits a fast analysis on square centimeters areas without the need for any precise (and expensive) scanning system. We present here accurate depth calibration which shows the potentiality of this instrument
OMNICAM: Bifocal Panoramic Camera for Human and Robotic Exploration
No full textSituational awareness is the key for maximizing the return of any operation, both for scientific and engineering assessments. SPACECLICK and INAF propose the OMNICAM, a novel camera system which can capture a 360° context view and an optically magnified portion of the same panorama with a single lens and sensor. The Bifocal Panoramic Lens (BPL) (designed by INAF researchers) is a lens capable of warping a panoramic Field-of-View (FoV) of 360° x 100° and simultaneously a round FoV of 20° in high-resolution. While the panoramic portion is always available for continuous monitoring surrounding environment, assets and ongoing operations, additionally the OMNICAM makes use of a pan/tilt mechanism to provide users of orientation capabilities for the magnified portion of the FoV. The small number of systems in OMNICAM leads to an overall reduction of weight and power consumption/complexity of redundant electronics as well as possible weak points. An ad-hoc developed software allows wireless r..
Surface measurements of radio antenna panels with white-light interferometry
No full textTypical radio telescopes have the primary reflector surface which is composed of several single panels that have dimensions of a meter a side. The manufacturing of these radio panels yield a micrometric precision over the volume on the single panel, hence the surface roughness of the panels can be measured with very high accuracy by means of the low coherence interferometry (LCI) technique which reaches micrometric spatial and depth resolution and has the advantage of being contact-less. We have developed a multi-channel partially coherent light interferometer to realize non contact 3D surface topography. The technique is based on the LCI principle, for which a bi-dimensional sensor - a CMOS - has been developed to directly acquire images. Tri-dimensional measures are recovered with a single scanning along the depth direction in a millimetric range, and every single pixel of the bi-dimensional sensor measures a point on the object, this allows a fast analysis in real time on square centimeter areas. In this paper we show the results obtained by applying the LCI technique method to analyze the surface roughness of the panels of a large radio antenna of 64 m of width and used for astronomical observations at 100 GHz; by measuring their 3D structure at micrometric resolution it is possible to verify their fabrication errors
A-central model for the geometric calibration of hyper-hemispherical lenses
Full text linkHyper-hemispherical lenses are optical objective lenses with an ultra-wide field of view. Due to their extreme field of view, the geometric calibration introduces several setup difficulties. Various methods have been developed for simplifying the geometric calibration of a camera in the close-range field by defining intrinsic and extrinsic calibration parameters in a limited ambience of a clean room and taking advantage of simple calibration chessboards. A well-known example in this regard is Zhang’s approach for pinhole cameras. A similar approach was pursued by Scaramuzza to model more extensive cameras that include fisheye and panoramic lenses. However, despite this toolbox’s efficiency, it is ineffectual in the case of a hyper-hemispherical lens because of model limitations in the approximation of the corresponding projection system. In this study, we define and validate what we believe to be a novel a-central model extension (AME) for the description of hyper-hemispherical lenses that is able to overcome these limitations and to describe more accurately the physical behavior introduced by the design of these lenses. For this apparently new a-central model, we obtain significantly improved calibration results for one of the cameras designed in our laboratory and planned to become a planetary payload of an ESA mission
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
- …
