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Principle of the Fresnel effect; the amount of reflection on a reflective surface depends on the viewing angle (A). When applied to spherical object; the edges exhibit strong reflections due to the shallow viewing angle (B). 

Principle of the Fresnel effect; the amount of reflection on a reflective surface depends on the viewing angle (A). When applied to spherical object; the edges exhibit strong reflections due to the shallow viewing angle (B). 

Source publication
Conference Paper
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The presence of depth cues in a visualization can be a great aid in understanding the structure and topology of a vessel tree. Pseudo Chromadepth is a well-known technique for enhancing depth perception in vascular 3D models. Since it strongly relies on the color channel to convey its depth cues, it is traditionally not suited for combined visualiz...

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Context 1
... on the current viewing direction. This type of shading is inspired by the Fresnel effect, which describes the amount of reflection and refraction of light on a surface in relation to the viewing angle. A flatter viewing angle on a surface increases the amount of light that is reflected, resulting in the surface appear- ing brighter when lighted (Fig. 4A). A physically accurate calculation of this effect is quite compli- cated, especially when taking into consideration that due to chro- matic dispersion, the strength of the Fresnel effect also depends on the light components' wavelengths. Instead, we use a simplified version of this effect to generate a mask for overlaying the PCD ...
Context 2
... PCD is dependent on the angle between the normal and inci- dent vectors, reaching its maximal value when they are orthogonal to each other. On spherical or tubular models, the Fresnel effect strongly increases the reflectiveness around the edges of the model (Fig. ...

Citations

... Applying pseudo chroma-depth to a whole mesh, however, impairs the ability to use other shading techniques to convey structure or to display additional information on the surface itself. To cope with this issue, Behrendt et al. [BBPS17] proposed to apply pseudo chroma-depth only to the contour region of a mesh to make space for supplementary data. Apart from colouring or texturing a given surface to convey data, additional geometry can be added as glyphs to an existing scene [ROP11]. ...
... The smaller the diameter of a vessel segment, the better can information from the contour represent the data of the affiliated vessel segment. For example, this has previously been done by Behrendt et al. [BBPS17], who encoded the depth of vasculature by colouring its contour using pseudo chroma-depth. Instead of defining the contour on the surface itself (e.g. by using a Fresnel approximation), we aim to create additional geometry at locations of the rendered mesh, where the surface normal is orthogonal to the view direction. ...
... Alternatively, the contour can simply be coloured w.r.t. the pseudo chroma-depth spectrum as in Figure 15, leaving the surface free for other encodings. This addresses an issue which has been tackled by Behrendt et al. [BBPS17]. They mixed the colour coding of a scalar field and pseudo chroma-depth using a Fresnel term. ...
Article
Full-text available
The study of vascular structures, using medical 3D models, is an active field of research. Illustrative visualizations have been applied to this domain in multiple ways. Researchers made the geometric properties of vasculature more comprehensive and augmented the surface with representations of multivariate clinical data. Techniques that head beyond the application of colour‐maps or simple shading approaches require a surface parameterization, that is, texture coordinates, in order to overcome locality. When extracting 3D models, the computation of texture coordinates on the mesh is not always part of the data processing pipeline. We combine existing techniques to a simple parameterization approach that is suitable for tree‐like structures. The parameterization is done w.r.t. to a pre‐defined source vertex. For this, we present an automatic algorithm, that detects the tree root. The parameterization is partly done in screen‐space and recomputed per frame. However, the screen‐space computation comes with positive features that are not present in object‐space approaches. We show how the resulting texture coordinates can be used for varying hatching, contour parameterization, display of decals, as additional depth cues and feature extraction. A further post‐processing step based on parameterization allows for a segmentation of the structure and visualization of its tree topology. The study of vascular structures, using medical 3D models, is an active field of research. Illustrative visualizations have been applied to this domain in multiple ways. Researchers made the geometric properties of vasculature more comprehensive and augmented the surface with representations of multivariate clinical data. Techniques that head beyond the application of colour‐maps or simple shading approaches require a surface parameterization, that is, texture coordinates, in order to overcome locality. When extracting 3D models, the computation of texture coordinates on the mesh is not always part of the data processing pipeline.
... Thus, we combine a 2D and 3D view of the vasculature to highlight clinically relevant properties in a clearer way. For example, the distance of vessel segments to tumor tissue inside a liver, which may aid analysis prior a tumor resection, or hemodynamics data [BBPS17]. A crucial factor that determines what kind of visualization techniques can be applied, is the type of data in which the vasculature is represented. ...
Conference Paper
Full-text available
In this paper, we make contributions to the visualization of vascular structures. Based on skeletal input data, we provide a combined 2D and implicit 3D visualization of vasculature, that is parameterized on-the-fly for illustrative visualization. We use an efficient algorithm that creates a distance field volume from triangles and extend it to handle skeletal tree data. Sphere-tracing this volume allows to visualize the vasculature in a flexible way, without the need to recompute the volume. Illustrative techniques, that have been frequently applied to vascular visualizations often require texture coordinates. Therefore, modifying an object-based algorithm, we propose an image-based, hierarchical optimization process that allows to derive periodic texture coordinates in a frame-coherent way and suits the implicit representation of the vascular structures. In addition to the 3D surface visualization, we propose a simple layout algorithm that applies a 2D parameterization to the skeletal tree nodes. This parameterization can be used to color-code the vasculature or to plot a 2D overview-graph, that highlights the branching topology of the skeleton. We transfer measurements, done in 3D space, to the 2D plot in order to avoid visual clutter and self occlusions in the 3D representation. A visual link between the 3D and 2D views is established via color codes and texture patterns. The potential of our pipeline is shown in several prototypical application scenarios.
... Winne et al., 2011, has used alternatively colored guiding lines for distance visualization [19]. Furthermore, Pseudo Chromadepth is a well known technique for depth perception in 3D angiography datasets, where the color gradient corresponds to the distance value at each point [20], [21]. Although, the technique enhances the relative distance perception between various points in cluttered angiography dataset, it doesn't give a real-time feedback for depth perception which is important during a real surgery. ...
Conference Paper
Augmented reality (AR) is a promising technology where the surgeon can see the medical abnormality in the context of the patient. It makes the anatomy of interest visible to the surgeon which otherwise is not visible. It can result in better surgical precision and therefore, potentially better surgical outcomes and faster recovery times. Despite these benefits, the current AR systems suffer from two major challenges; first, incorrect depth perception and, second, the lack of suitable evaluation systems. Therefore, in the current paper we addressed both of these problems. We proposed a color depth encoding (CDE) technique to estimate the distance between the tumor and the tissue surface using a surgical instrument. We mapped the distance between the tumor and the tissue surface to the blue-red color spectrum. For evaluation and interaction with our AR technique, we propose to use a virtual surgical instrument method using the CAD model of the instrument. The users were asked to reach the judged distance in the surgical field using the virtual tool. Realistic tool movement was simulated by collecting the forward kinematics joint encoder data. The results showed significant improvement in depth estimation, time for task completion and confidence, using our CDE technique with and without stereo versus other two cases, that are, Stereo-No CDE and No Stereo-No CDE.
... Such information contains for instance additionally acquired or derived parameters such as blood flow, pressure or wall shear stress, which are typically conveyed by stream lines, different color scales or glyphs. Effectively communicating all this information without overwhelming the viewer is a problem that has been addressed by several authors in the past [2,17,19,30]. ...
... Thus, various approaches have been considered to overcome this problem. Behrendt et al. [2] introduced a technique to encode information on the vessels whilst maintaining the benefits of the pseudo-chromadepth color scale, by applying it on the edges of the vessels only. Lichtenberg et al. [19] used glyphs to communicate depth information on the vessel end-points freeing the surface of the vessel of such task. ...
... Domain experts are often interested in visualizing also other properties on top of the vessels. This problem was addressed by Behrendt et al. [2] who combined pseudo-chromadepth with additional information on top of the vessels. They used the pseudo-chromadepth color scheme to shade the areas close to the contour by applying a blending mask inspired by Fresnel equations. ...
Preprint
To enhance depth perception and thus data comprehension, additional depth cues are often used in 3D visualizations of complex vascular structures. Accordingly, there is a variety of different approaches described in the literature, ranging from chromadepth color coding over depth of field to glyph-based encodings. Unfortunately, the majority of existing approaches suffers from the same problem. As these cues are directly applied to the geometry's surface, the display of additional information, such as other modalities or derived attributes, associated with a vessel is impaired. To overcome this limitation we propose Void Space Surfaces which utilize the empty space in between vessel branches to communicate depth and their relative positioning. This allows us to enhance the depth perception of vascular structures without interfering with the spatial data and potentially superimposed parameter information. Within this paper we introduce Void Space Surfaces, describe their technical realization, and show their application to various vessel trees. Moreover, we report the outcome of a user study which we have conducted in order to evaluate the perceptual impact of Void Space Surfaces as compared to existing vessel visualization techniques.
... Applying chromadepth to a 3D surface makes it difficult to additionally encode attributes on the surface. Therefore, Behrendt et al. [22] used the Fresnel term to combine chromadepth and additional parameters. Illustrative techniques were also used to improve depth perception. ...
... In the first step a novel technique is developed. Applying illustrative techniques [7,23,26] , glyphs [27] , or add an additional layer of information [22,28] can improve depth perception, whereas methods aiming at improving shape perception of surfaces use, e.g., Phong shading [34] or line drawings [33] . The last step reveals the potential benefits of the novel technique. ...
Article
To enhance depth perception and thus data comprehension, additional depth cues are often used in 3D visualizations of complex vascular structures. There is a variety of different approaches described in the literature, ranging from chromadepth color coding over depth of field to glyph-based encodings. Unfortunately, the majority of existing approaches suffers from the same problem: As these cues are directly applied to the geometry's surface, the display of additional information on the vessel wall, such as other modalities or derived attributes, is impaired. To overcome this limitation we propose Void Space Surfaces which utilizes empty space in between vessel branches to communicate depth and their relative positioning. This allows us to enhance the depth perception of vascular structures without interfering with the spatial data and potentially superimposed parameter information. With this paper, we introduce Void Space Surfaces, describe their technical realization, and show their application to various vessel trees. Moreover, we report the outcome of two user studies which we have conducted in order to evaluate the perceptual impact of Void Space Surfaces compared to existing vessel visualization techniques and discuss expert feedback.
Article
User studies are indispensable for visualization application papers in order to assess the value and limitations of the presented approach. Important aspects are how well depth and shape information can be perceived, as coding of these aspects is essential to enable an understandable representation of complex 3D data. In practice, there is usually little time to perform such studies, and the establishment and conduction of user studies can be labour-intensive. In addition, it can be difficult to reach enough participants to obtain expressive results regarding the quality of different visualization techniques. In this paper, we propose a framework that allows visualization researchers to quickly create task-based user studies on depth and shape perception for different surface visualizations and perform the resulting tasks via a web interface. With our approach, the effort for generating user studies is reduced and at the same time the web-based component allows researchers to attract more participants to their study. We demonstrate our framework by applying shape and depth evaluation tasks to visualizations of various surface representations used in many technical and biomedical applications.
Conference Paper
Full-text available
The study and visualization of vascular structures, using 3D models obtained from medical data, is an active field of research. Illustrative visualizations have been applied to this domain in multiple ways. Researchers have tried to make the geometric properties of vasculature more comprehensive and to augment the surface with representations of multivariate clinical data. Techniques that head beyond the application of color-maps or simple shading approaches require a sort of surface parameterization, i.e., texture coordinates, in order to overcome locality. When extracting 3D models, the computation of texture coordinates on the mesh is not always part of the data processing pipeline. We combine existing techniques to a simple, yet effective, parameterization approach that is suitable for tree-like structures. The parameterization is done w.r.t. to a pre-defined source vertex. For this, we present an automatic algorithm, that detects the root of a tree-structure. The parameterization is partly done in screen-space and recomputed per frame. However, the screen-space computation comes with positive features that are not present in object-space approaches. We show how the resulting texture coordinates can be used for varying hatching, contour parameterization, the display of decals, as an additional depth cue and feature extraction. Source Code can be found at: https://gitlab.uni-koblenz.de/MedVis/PFE_Tree-like_Structures