Parallax

About: Parallax is a research topic. Over the lifetime, 6014 publications have been published within this topic receiving 84282 citations. The topic is also known as: parallax effect.

Gaia Data Release 2: The astrometric solution

Abstract: Context. Gaia Data Release 2 (Gaia DR2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 22 months of its operational phase.Aims. We describe the input data, models, and processing used for the astrometric content of Gaia DR2, and the validation of these resultsperformed within the astrometry task.Methods. Some 320 billion centroid positions from the pre-processed astrometric CCD observations were used to estimate the five astrometric parameters (positions, parallaxes, and proper motions) for 1332 million sources, and approximate positions at the reference epoch J2015.5 for an additional 361 million mostly faint sources. These data were calculated in two steps. First, the satellite attitude and the astrometric calibration parameters of the CCDs were obtained in an astrometric global iterative solution for 16 million selected sources, using about 1% of the input data. This primary solution was tied to the extragalactic International Celestial Reference System (ICRS) by means of quasars. The resulting attitude and calibration were then used to calculate the astrometric parameters of all the sources. Special validation solutions were used to characterise the random and systematic errors in parallax and proper motion.Results. For the sources with five-parameter astrometric solutions, the median uncertainty in parallax and position at the reference epoch J2015.5 is about 0.04 mas for bright (G = 17 mag, and 0.7 masat G = 20 mag. In the proper motion components the corresponding uncertainties are 0.05, 0.2, and 1.2 mas yr−1 , respectively.The optical reference frame defined by Gaia DR2 is aligned with ICRS and is non-rotating with respect to the quasars to within 0.15 mas yr−1 . From the quasars and validation solutions we estimate that systematics in the parallaxes depending on position, magnitude, and colour are generally below 0.1 mas, but the parallaxes are on the whole too small by about 0.03 mas. Significant spatial correlations of up to 0.04 mas in parallax and 0.07 mas yr−1 in proper motion are seen on small ( DR2 astrometry are given in the appendices.

Single lens stereo with a plenoptic camera

Abstract: Ordinary cameras gather light across the area of their lens aperture, and the light striking a given subregion of the aperture is structured somewhat differently than the light striking an adjacent subregion. By analyzing this optical structure, one can infer the depths of the objects in the scene, i.e. one can achieve single lens stereo. The authors describe a camera for performing this analysis. It incorporates a single main lens along with a lenticular array placed at the sensor plane. The resulting plenoptic camera provides information about how the scene would look when viewed from a continuum of possible viewpoints bounded by the main lens aperture. Deriving depth information is simpler than in a binocular stereo system because the correspondence problem is minimized. The camera extracts information about both horizontal and vertical parallax, which improves the reliability of the depth estimates. >

A new sense for depth of field

Abstract: One of the major unsolved problems in designing an autonomous agent [robot] that must function in a complex, moving environment is obtaining reliable, real-time depth information, preferably without the limitations of active scanners. Stereo remains computationally intensive and prone to severe errors, the use of motion information is still quite experimental, and autofocus schemes can measure depth at only one point at a time. We examine a novel source of depth information: focal gradients resulting from the limited depth of field inherent in most optical systems. We prove that this source of information can be used to make reliable depth maps of useful accuracy with relatively minimal computation. Experiments with realistic imagery show that measurement of these optical gradients can potentially provide depth information roughly comparable to stereo disparity or motion parallax, while avoiding image-to-image matching problems. A potentially real-time version of this algorithm is described.

The parallax view

Abstract: The Parallax View is Slavoj Zizek's most substantial theoretical work to appear in many years; Zizek himself describes it as his magnum opus. Parallax can be defined as the apparent displacement of an object, caused by a change in observational position. Zizek is interested in the "parallax gap" separating two points between which no synthesis or mediation is possible, linked by an "impossible short circuit" of levels that can never meet. From this consideration of parallax, Zizek begins a rehabilitation of dialectical materialism.Modes of parallax can be seen in different domains of today's theory, from the wave-particle duality in quantum physics to the parallax of the unconscious in Freudian psychoanalysis between interpretations of the formation of the unconscious and theories of drives. In The Parallax View, Zizek, with his usual astonishing erudition, focuses on three main modes of parallax: the ontological difference, the ultimate parallax that conditions our very access to reality; the scientific parallax, the irreducible gap between the phenomenal experience of reality and its scientific explanation, which reaches its apogee in today's brain sciences (according to which "nobody is home" in the skull, just stacks of brain meat--a condition Zizek calls "the unbearable lightness of being no one"); and the political parallax, the social antagonism that allows for no common ground. Between his discussions of these three modes, Zizek offers interludes that deal with more specific topics--including an ethical act in a novel by Henry James and anti-anti-Semitism.The Parallax View not only expands Zizek's Lacanian-Hegelian approach to new domains (notably cognitive brain sciences) but also provides the systematic exposition of the conceptual framework that underlies his entire work. Philosophical and theological analysis, detailed readings of literature, cinema, and music coexist with lively anecdotes and obscene jokes.

A New Sense for Depth of Field

Abstract: This paper examines a novel source of depth information: focal gradients resulting from the limited depth of field inherent in most optical systems. Previously, autofocus schemes have used depth of field to measured depth by searching for the lens setting that gives the best focus, repeating this search separately for each image point. This search is unnecessary, for there is a smooth gradient of focus as a function of depth. By measuring the amount of defocus, therefore, we can estimate depth simultaneously at all points, using only one or two images. It is proved that this source of information can be used to make reliable depth maps of useful accuracy with relatively minimal computation. Experiments with realistic imagery show that measurement of these optical gradients can provide depth information roughly comparable to stereo disparity or motion parallax, while avoiding image-to-image matching problems.