The last decades a variety of portable or wearable navigation systems have been developed to assist visually impaired people during navigation in known or unknown, indoor or outdoor environments. There are three main categories of these systems: electronic travel aids (ETAs), electronic orientation aids (EOAs), and position locator devices (PLDs). This paper presents a comparative survey among portable/wearable obstacle detection/avoidance systems (a subcategory of ETAs) in an effort to inform the research community and users about the capabilities of these systems and about the progress in assistive technology for visually impaired people. The survey is based on various features and performance parameters of the systems that classify them in categories, giving qualitative-quantitative measures. Finally, it offers a ranking, which will serve only as a reference point and not as a critique on these systems.

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Wearable Obstacle Avoidance Electronic Travel Aids for Blind: A Survey

Indoor Human Navigation Systems {a Survey

This paper introduces importance-driven volume rendering as a novel technique for automatic focus and context display of volumetric data. Our technique is a generalization of cut-away views, which - depending on the viewpoint - remove or suppress less important parts of a scene to reveal more important underlying information. We automatize and apply this idea to volumetric data. Each part of the volumetric data is assigned an object importance which encodes visibility priority. This property determines which structures should be readily discernible and which structures are less important. In those image regions, where an object occludes more important structures it is displayed more sparsely than in those areas where no occlusion occurs. Thus the objects of interest are clearly visible. For each object several representations, i.e., levels of sparseness, are specified. The display of an individual object may incorporate different levels of sparseness. The goal is to emphasize important structures and to maximize the information content in the final image. This paper also discusses several possible schemes for level of sparseness specification and different ways how object importance can be composited to determine the final appearance of a particular object.

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Importance-Driven Volume Rendering

Visualization in Medicine is the first book on visualization and its application to problems in medical diagnosis, education, and treatment. The book describes the algorithms, the applications and their validation (how reliable are the results?), and the clinical evaluation of the applications (are the techniques useful?). It discusses visualization techniques from research literature as well as the compromises required to solve practical clinical problems. 

The book covers image acquisition, image analysis, and interaction techniques designed to explore and analyze the data. The final chapter shows how visualization is used for planning liver surgery, one of the most demanding surgical disciplines. The book is based on several years of the authors' teaching and research experience. Both authors have initiated and lead a variety of interdisciplinary projects involving computer scientists and medical doctors, primarily radiologists and surgeons.

* A core field of visualization and graphics missing a dedicated book until now
* Written by pioneers in the field and illustrated in full color
* Covers theory as well as practice

Visualization in Medicine: Theory, Algorithms, and Applications

We propose clipping methods that are capable of using complex geometries for volume clipping. The clipping tests exploit per-fragment operations on the graphics hardware to achieve high frame rates. In combination with texture-based volume rendering, these techniques enable the user to interactively select and explore regions of the data set. We present depth-based clipping techniques that analyze the depth structure of the boundary representation of the clip geometry to decide which parts of the volume have to be clipped. In another approach, a voxelized clip object is used to identify the clipped regions. Furthermore, the combination of volume clipping and volume shading is considered. An optical model is introduced to merge aspects of surface-based and volume-based illumination in order to achieve a consistent shading of the clipping surface. It is demonstrated how this model can be efficiently incorporated in the aforementioned clipping techniques.

Interactive clipping techniques for texture-based volume visualization and volume shading

In this paper we present a new system that assists blind users in orienting themselves in indoor environments. We developed a sensor module that can be handled like a flashlight by a blind user and can be used for searching tasks within the three-dimensional environment. By pressing keys, inquiries concerning object characteristics, position, orientation and navigation can be sent to a connected portable computer, or to a federation of data servers providing models of the environment. Finally these inquiries are acoustically answered over a text-to-speech engine.

Design and development of an indoor navigation and object identification system for the blind

In this paper we discuss different approaches to generate cutaway illustrations. The purpose of such a drawing is to allow the viewer to have a look into an otherwise solid opaque object. Traditional methods to draw these kinds of illustrations are evaluated to extract a small and effective set of rules for a computer-based rendering of cutaway illustrations. We show that our approaches are not limited to a specific rendering style but can be successfully combined with a great variety of well-known artistic or technical illustration techniques. All methods of this paper make use of modern graphics hardware functionality to achieve interactive frame rates.

Interactive Cutaway Illustrations

This paper describes how technical illustrations containing opaque and non-opaque objects can be automatically generated. Traditional methods to show transparency in manual drawings are evaluated to extract a small and effective set of rules for computer-based rendering of technical illustrations, leading to a novel view-dependent transparency model. We propose a hardware-accelerated depth sorting algorithm in image-space which specifically meets the requirements of our transparency model. In this way, real-time rendering of semi-transparent technical illustrations is achieved. Finally, it is described how our approach can be combined with other methods in the field of non-photorealistic rendering in order to enhance the visual perception of technical illustrations.

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Transparency in Interactive Technical Illustrations

There is a growing interest for providing interactive graphics also on mobile devices like PDAs, Smartphones, etc. Right now mobile devices are very limited concerning graphical resources basically only simple 2D rasterization operations are available, that run completely on the main CPU of the device. The desire to have more complex 3D graphics on these devices often results in a remote rendering solution. Classical remote rendering solutions produce the final images on a server and transfer these to the client device over a wired or nonwired network. We present an alternative method to the image-based approach by splitting the rendering process between client and server transfering couple of 2D line primitives over the network, which are rendered locally by the mobile device

Remote line rendering for mobile devices

With the advent of generic remote visualization solutions, accessing distant graphics resources from the desktop is no longer restricted to specially tailored applications. However, current solutions still suffer from poor interactivity due to limited network bandwidth and high latency. In this paper we present several improvements to our remote visualization system in order to overcome these drawbacks. Different image compression schemes are evaluated with regard to applicability for scientific visualization, showing that image compression alone cannot guarantee interactive frame rates. Therefore, we furthermore present different techniques for alleviating the bandwidth limit, including quality reduction during user interaction or animations. Latency aspects are addressed by employing multi-threading for asynchronous compression and utilizing features of modern programmable graphics adapters for performing the image compression entirely or the graphics card. The presented ideas are integrated in our remote visualization system without violating universality.

Joachim Diepstraten

Papers

Design and development of an indoor navigation and object identification system for the blind

Interactive Cutaway Illustrations

Transparency in Interactive Technical Illustrations

Remote line rendering for mobile devices

Widening the remote visualization bottleneck