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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Rendering techniques generally involve setting a color or color function across each component, often based on the effects of a light source from the observer to the screen. For example, a square polygon facing the observer may be red, while its color may change toward darker shades of red as the polygon is rotated, becoming completely dark when 90° from the observer. Shading techniques may compute color as a continuous function across a component. Gouraud shading, for example, interpolates a color value across a polygon from its corner values, while another technique known as Phong shading computes color from an interpolation of the light source vector itself across the polygon. More advanced rendering techniques include ray tracing, which computes the behavior of light rays to simulate effects such as reflectance, shadows, and translucency, and texture mapping, which simulates a pattern or image across surfaces of the displayed model.
Interactive, in-browser cinematic volume rendering of medical images
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2023
Jiayi Xu, Gaspard Thevenon, Timothee Chabat, Matthew McCormick, Forrest Li, Tom Birdsong, Ken Martin, Yueh Lee, Stephen Aylward
Gradient-based shading is one of the most widely used methods to capture surface reflection. It is based on the normalised surface gradient, and in terms of medical data, the gradient of scalar values. Surface lighting has many advantages: relatively low time complexity compared to scattering, realistic surface lighting effect and easy adaptation to any lighting scenario. It allows clinicians to quickly capture information such as surface orientation and reflection. However, gradient-based shading only takes adjacent voxels into account, and thus is unable to capture the scattering effects of translucent materials or media occlusions. For gradient-based method, we replace the in-scattering term in Equation (1) with the Phong Shading model (Phong 1975), formulated as:
The Effect of Interactive Cues on the Perception of Angiographic Volumes in Virtual Reality
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2021
Andrey Titov, Marta Kersten-Oertel, Simon Drouin
Ropinski et al. (2006) performed a user study where they compared the effectiveness in depth perception of previously studied techniques such as edge enhancement, Phong shading, depth of field (DoF), stereoscopy, chromadepth, and pseudo-chromadepth. It was determined that pseudo-chromadepth performs better than full chroma, and is the best shading technique in terms of decision time. However, in terms of correctness, the overlaid edges technique was found to be better than pseudo-chromadepth. In a similar study, Kersten-Oertel et al. (2014) compared the effectiveness of kinetic depth, stereoscopy, edge, pseudo-chromadepth and fog for novices and experts. It was determined that pseudo-chromadepth generally resulted in the best decision time and correctness, similar to the results obtained by Ropinski et al. (2006). It was also found that the edge cue was more helpful to experts than novices. Kreiser et al. (2018) introduced the concept of Void Space Surfaces (VSS) that encode the depth of vessels in the scene using the surrounding background. They then compared the chromadepth and pseudo-chroma versions of VSS to directly applied versions of these cues (to the surface of the vessels) using standard Phong shading as the base case. Although directly applied cues and VSS resulted in similar correctness, they both performed better than Phong. In terms of decision time, direct cues performed better than Phong, while VSS performed worse. The results of this study regarding the effectiveness of pseudo-chromadepth slightly differ from those obtained by Ropinski et al. (2006) and Kersten-Oertel et al. (2014) in that pseudo-chromadepth was not found to be more effective than chromadepth.