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Explosive Flows: Shock Tubes and Blast Waves
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
Cameras and light sources for shock-wave photogrammetry are characterized by the need for high framing rates and short exposure times in order to freeze the supersonic shocks. Until the advent of the pulsed laser, a spark source was the most economical method of achieving the required intensity and short duration [13]. By 1929 Cranz and Schardin [108] had developed a multiple-spark system for photographing shock waves, in which 24 separate sparks and optical systems were used to record 24 images on a single photographic plate, with frequencies up to 50 kHz. With modern triggering mechanisms, there is virtually no limit to the frequency at which sparks can be initiated. The Cranz–Schardin system is still widely used, and recent developments to the technique are described in Refs. [109–111]. Because a separate optical system is used for each picture, individual parallax corrections must be made if accurate measurements are required from the sequence of photographs.
Designing for Telepresence: The Delft Virtual Window System
Published in Peter Hancock, John Flach, Jeff Caird, Kim Vicente, Local Applications of the Ecological Approach to Human-Machine Systems, 2018
In accordance with the distinction between motion and movement, we differentiate between motion parallax and movement parallax. This difference is comparable to Sedgwick′s (1986) distinction between relative and absolute motion parallax. Parallax refers to the fact that when two objects are at different distances from a moving observation point, the objects seem to shift relative to each other. We speak of movement parallax when the movement of the observation point is self-generated, and of motion parallax when this motion is imposed. Suppose that one is walking in the countryside and looking at the landscape. Let us also suppose that the gaze direction is perpendicular to the moving direction, that the direction of movement is from right to left, and that one is gazing at a fixation point. Under these conditions, all of the objects closer to the observer than the fixation point would appear to move in a direction opposite to his or her movement. On the other hand, objects that are further away will appear to move in the same direction the observer is moving. Not only the direction, but also the the speed of movement varies with the object′s proximity to his or her fixation point and movement speed and direction. This is movement parallax. Motion parallax contains the part of it used by a cinematographer. He or she uses the apparent movements around the fixation point as registered by camera movements, without them being linked to the spectators′ movements.
Alignment and Angle Measurement Techniques
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
In telescopic sights for measurement, a graticule is fitted in the image plane for setting or measuring. Here the sharpness of definition is not the only consideration; the image of the object (the target) should also lie in the graticule plane or should be close enough so that there is no parallax between the image and the graticule. When the parallax is present, the coincidence of the image depends on position of the eye; measurement error is the result. The problem is shown in Fig. 5.1. To remove parallax, the eyepiece is adjusted first until the graticule is seen clearly. One then focuses on the object by the appropriate focusing mechanism. Parallax is tested by the movement of the eye behind the eyepiece, and focusing is continued until relative movement between the object and the graticule lines is removed..
Effects of Visual Cues on Distance Perception in Virtual Environments Based on Object Identification and Visually Guided Action
Published in International Journal of Human–Computer Interaction, 2021
Sunyoung Ahn, Sangyeon Kim, Sangwon Lee
In a VE, four types of depth cues are typically considered: oculomotor, binocular, monocular, and motion-based depth cues (Cutting, 1997; Reichelt et al., 2010; Sherman & Craig, 2002). Oculomotor refers to physiological depth cues that consist of accommodation (eye focus) and convergence (eye rotation angle). Binocular depth cues are related to different images presented by both sides of VR displays according to the retinal disparity of both eyes. Monocular depth cues are the static and classic pictorial cues such as interpositions (also called occlusion), shadings, related or known sizes, linear perspectives, surface texture gradients (or relative densities), heights in a visual field, atmospheric effects, and brightness. Based on monocular depth cues, users can detect depth information even with a single eye. Motion-based depth cues, known as motion parallax, refer to the relative movement of images across the retina resulting from the movement of a user or an object.