EGVE06: 12th Eurographics Symposium on Virtual Environments

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https://diglib.eg.org/handle/10.2312/371

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Model-based Hybrid Tracking for Medical Augmented Reality
(The Eurographics Association, 2006) Fischer, Jan; Eichler, Michael; Bartz, Dirk; Straßer, Wolfgang; Ming Lin and Roger Hubbold
Camera pose estimation is one of the most important, but also one of the most challenging tasks in augmented reality. Without a highly accurate estimation of the position and orientation of the digital video camera, it is impossible to render a spatially correct overlay of graphical information. This requirement is even more crucial in medical applications, where the virtual objects are supposed to be correctly aligned with the patient. Many medical AR systems use specialized tracking devices, which can be of limited suitability for real-world scenarios. We have developed an AR framework for surgical applications based on existing medical equipment. A surgical navigation device delivers tracking information measured by a built-in infrared camera system, which is the basis for the pose estimation of the AR video camera. However, depending on the conditions in the environment, this infrared pose data can contain discernible tracking errors. One main drawback of the medical tracking device is the fact that, while it delivers a very high positional accuracy, the reported camera orientation can contain a relatively large error. In this paper, we present a hybrid tracking scheme for medical augmented reality based on a certified medical tracking system. The final pose estimation takes the inital infrared tracking data as well as salient features in the camera image into account. The vision-based component of the tracking algorithm relies on a pre-defined graphical model of the observed scene. The infrared and vision-based tracking data are tightly integrated into a unified pose estimation algorithm. This algorithm is based on an iterative numerical optimization method. We describe an implementation of the algorithm and present experimental data showing that our new method is capable of delivering a more accurate pose estimation.
A Survey and Taxonomy of 3D Menu Techniques
(The Eurographics Association, 2006) Dachselt, R.; Hübner, A.; Ming Lin and Roger Hubbold
A huge variety of interaction techniques was developed in the field of virtual and augmented reality. Whereas techniques for object selection, manipulation, travel, and wayfinding were covered in existing taxonomies quite in detail, application control techniques were not sufficiently deliberated yet. However, they are needed by almost every mixed reality application, e.g. for choosing from alternative objects or options. For this purpose a great variety of distinct three-dimensional menu selection techniques is available. This paper surveys existing 3D menus from the corpus of literature and classifies them according to various criteria. The taxonomy introduced here assists developers of interactive 3D applications to better evaluate their options when choosing and implementing a 3D menu technique. Since the taxonomy spans the design space for 3D menu solutions, it also aids researchers in identifying opportunities to improve or create novel virtual menu techniques.
A Model for the Expected Running Time of Collision Detection using AABB Trees
(The Eurographics Association, 2006) Weller, René; Klein, Jan; Zachmann, Gabriel; Ming Lin and Roger Hubbold
In this paper, we propose a model to estimate the expected running time of hierarchical collision detection that utilizes AABB trees, which are a frequently used type of bounding volume (BV). We show that the average running time for the simultaneous traversal of two binary AABB trees depends on two characteristic parameters: the overlap of the root BVs and the BV diminishing factor within the hierarchies. With this model, we show that the average running time is in O(n) or even in O(logn) for realistic cases. Finally, we present some experiments that confirm our theoretical considerations. We believe that our results are interesting not only from a theoretical point of view, but also for practical applications, e. g., in time-critical collision detection scenarios where our running time prediction could help to make the best use of CPU time available.
Interactive Data Annotation in Virtual Environments
(The Eurographics Association, 2006) Assenmacher, I.; Hentschel, B.; Ni, C.; Kuhlen, T.; Bischof, C.; Ming Lin and Roger Hubbold
Note-taking is an integral part of scientific data analysis. In particular, it is vital for explorative analysis, as the expression and transformation of ideas is a necessary precondition for gaining insight. However, in the case of interactive data exploration in virtual environments it is not possible to keep a pen and pencil at hand. Additionally, data analysis in virtual environments allows the multi-modal exploration of complex and time varying data. We propose the toolkit independent content generation system IDEA that features a defined process model, a generic annotation model with a variety of content types as well as specially developed interaction metaphors for their input and output handling. This allows the user to note ideas, e.g., in form of text, images or voice without interfering with the analysis process. In this paper we present the basic concepts for this system. We describe the context-content model which allows to tie annotation content to logical objects that are part of the scene and stores specific information for the special interaction in virtual environments. The IDEA system is already applied in a prototypical implementation for the exploration of air flows in the human nasal cavity where it is used for data analysis as well as interdisciplinary communication.
Fast Continuous Collision Detection among Deformable Models using Graphics Processors
(The Eurographics Association, 2006) Govindaraju, Naga K.; Kabul, Ilknur; Lin, Ming C.; Manocha, Dinesh; Ming Lin and Roger Hubbold
We present an interactive algorithm to perform continuous collision detection between general deformable models using graphics processors (GPUs). We model the motion of each object in the environment as a continuous path and check for collisions along the paths. Our algorithm precomputes the chromatic decomposition for each object and uses visibility queries on GPUs to quickly compute potentially colliding sets of primitives. We introduce a primitive classification technique to perform efficient continuous self-collision. We have implemented our algorithm on a 3:0 GHz Pentium IV PC with a NVIDIA 7800 GPU, and we highlight its performance on complex simulations composed of several thousands of triangles. In practice, our algorithm is able to detect all contacts, including self-collisions, at image-space precision in tens of milli-seconds.
Camera Setup Optimization for Optical Tracking in Virtual Environments
(The Eurographics Association, 2006) Cerfontaine, Philippe A.; Schirski, Marc; Bündgens, Daniel; Kuhlen, Torsten; Ming Lin and Roger Hubbold
In this paper we present a method for finding the optimal camera alignment for a tracking system with multiple cameras, by specifying the volume that should be tracked and an initial camera setup. The approach we use is twofold: on the one hand, we use a rather simple gradient based steepest descent method and on the other hand, we also implement a simulated annealing algorithm that features guaranteed optimality assertions. Both approaches are fully automatic and take advantage of modern graphics hardware since we implemented a GPU-based accelerated visibility test. The proposed algorithms can automatically optimize the whole camera setup by adjusting the given set of parameters. The optimization may have different goals depending on the desired application, e.g. one may wish to optimize towards the widest possible coverage of the specified volume, while others would prefer to maximize the number of cameras seeing a certain area to overcome heavy occlusion problems during the tracking process. Our approach also considers parameter constraints that the user may specify according to the local environment where the cameras have to be set up. This makes it possible to simply formulate higher level constraints e.g. all cameras have a vertical up vector. It individually adapts the optimization to the given situation and also asserts the feasibility of the algorithm s output.
Measuring the Discernability of Virtual Objects in Conventional and Stylized Augmented Reality
(The Eurographics Association, 2006) Fischer, Jan; Cunningham, Douglas; Bartz, Dirk; Wallraven, Christian; Bülthoff, Heinrich; Straßer, Wolfgang; Ming Lin and Roger Hubbold
In augmented reality, virtual graphical objects are overlaid over the real environment of the observer. Conventional augmented reality systems normally use standard real-time rendering methods for generating the graphical representations of virtual objects. These renderings contain the typical artifacts of computer generated graphics, e.g., aliasing caused by the rasterization process and unrealistic, manually configured illumination models. Due to these artifacts, virtual objects look artifical and can easily be distinguished from the real environment. A different approach to generating augmented reality images is the basis of stylized augmented reality [FBS05c]. Here, similar types of artistic or illustrative stylization are applied to the virtual objects and the camera image of the real enviroment. Therefore, real and virtual image elements look significantly more similar and are less distinguishable from each other. In this paper, we present the results of a psychophysical study on the effectiveness of stylized augmented reality. In this study, a number of participants were asked to decide whether objects shown in images of augmented reality scenes are virtual or real. Conventionally rendered as well as stylized augmented reality images and short video clips were presented to the participants. The correctness of the participants responses and their reaction times were recorded. The results of our study show that an equalized level of realism is achieved by using stylized augmented reality, i.e., that it is significantly more difficult to distinguish virtual objects from real objects.
Managing Missed Interactions in Distributed Virtual Environments
(The Eurographics Association, 2006) Parkin, S. E.; Andras, P.; Morgan, G.; Ming Lin and Roger Hubbold
A scalable distributed virtual environment (DVE) may be achieved by ensuring virtual world objects communicate their actions to only those objects that fall within their influence, reducing the need to send and process unnecessary messages. A missed interaction may be defined as a failure to exchange messages to appropriately model object interaction. A number of parameters under the control of a DVE developer may influence the possibility of missed interactions occurring (e.g., object velocities, area of influence). However, due to the complexities associated with object movement and the deployment environment (e.g., non-deterministic object movement, network latency), identifying the value for such parameters to minimise missed interactions while maintaining scalability (minimal message passing) is not clear. We present in this paper a tool which simulates a DVE and provides developers with an indication of the appropriate values for parameters when balancing missed interactions against scalability.
A New View Management Method for Wearable Augmented Reality Systems - Emphasizing the User-viewed Object and the Corresponding Annotation -
(The Eurographics Association, 2006) Tenmoku, R.; Kanbara, M.; Yokoya, N.; Ming Lin and Roger Hubbold
This paper describes a new view management method for annotation overlay using augmented reality(AR) systems. The proposed method emphasizes the user-viewed object and the corresponding annotation in order to present links between annotations and real objects clearly. This method includes two kinds of techniques for emphasizing the user-viewed object and the annotation. First, the proposed method highlights the object which is gazed at by the user using a 3D model without textures. Secondly, when the user-viewed object is occluded by other objects, the object is complemented by using an image made from a detailed 3D model with textures. This paper also describes experiments which show the feasibility of the proposed method by using a prototype wearable AR system.
GraphTracker: A Topology Projection Invariant Optical Tracker
(The Eurographics Association, 2006) Smit, F. A.; Rhijn, A. van; Liere, R. van; Ming Lin and Roger Hubbold
In this paper, we describe a new optical tracking algorithm for pose estimation of interaction devices in virtual and augmented reality. Given a 3D model of the interaction device and a number of camera images, the primary difficulty in pose reconstruction is to find the correspondence between 2D image points and 3D model points. Most previous methods solved this problem by the use of stereo correspondence. Once the correspondence problem has been solved, the pose can be estimated by determining the transformation between the 3D point cloud and the model. Our approach is based on the projective invariant topology of graph structures. The topology of a graph structure does not change under projection: in this way we solve the point correspondence problem by a subgraph matching algorithm between the detected 2D image graph and the model graph. There are four advantages to our method. First, the correspondence problem is solved entirely in 2D and therefore no stereo correspondence is needed. Consequently, we can use any number of cameras, including a single camera. Secondly, as opposed to stereo methods, we do not need to detect the same model point in two different cameras, and therefore our method is much more robust against occlusion. Thirdly, the subgraph matching algorithm can still detect a match even when parts of the graph are occluded, for example by the users hands. This also provides more robustness against occlusion. Finally, the error made in the pose estimation is significantly reduced as the amount of cameras is increased.
A Multi Modal Table-Top 3D Modeling Tool in Augmented Environments
(The Eurographics Association, 2006) Novotny, Tom; Lindt, Irma; Broll, Wolfgang; Ming Lin and Roger Hubbold
Even with today's highly sophisticated 3D modeling programs, creating, assembling and adapting 3D models is still a big challenge for inexperienced users. In this paper we present our approach of an intuitive table-top 3D modeling tool in Augmented Reality. It allows the author to view 3D virtual objects within his natural working environment, to manipulate them and to create new 3D elements easily. The offered interaction techniques support the author's activity by a combination of tangible user interfaces with voice recognition, a gaze-based view pointer and 3D widgets as components of a multi modal user interface. Within the scope of this work, intuitive interaction techniques were realized to offer the participants an easy way of working within an augmented environment. User tests were performed to compare our approach to a WIMP-based desktop application and to an alternative AR modeling application.
Hybrid Interfaces in VEs: Intent and Interaction
(The Eurographics Association, 2006) Haan, Gerwin de; Griffith, Eric J.; Koutek, Michal; Post, Frits H.; Ming Lin and Roger Hubbold
Hybrid user interfaces (UIs) integrate well-known 2D user interface elements into the 3D virtual environment, and provide a familiar and portable interface across a variety of VR systems. However, their usability is often reduced by accuracy and speed, caused by inaccuracies in tracking and a lack of constraints and feedback. To ease these difficulties often large widgets and bulky interface elements must be used, which, at the same time, limit the size of the 3D workspace and restrict the space where other supplemental 2D information can be displayed. In this paper, we present two developments addressing this problem: supportive user interaction and a new implementation of a hybrid interface. First, we describe a small set of tightly integrated 2D windows we developed with the goal of providing increased flexibility in the UI and reducing UI clutter. Next we present extensions to our supportive selection technique, IntenSelect. To better cope with a variety of VR and UI tasks, we extended the selection assistance technique to include direct selection, spring-based manipulation, and specialized snapping behavior. Finally, we relate how the effective integration of these two developments eases some of the UI restrictions and produces a more comfortable VR experience.
Friction surfaces: scaled ray-casting manipulation for interacting with 2D GUIs
(The Eurographics Association, 2006) Andujar, C.; Argelaguet, F.; Ming Lin and Roger Hubbold
The accommodation of conventional 2D GUIs with Virtual Environments (VEs) can greatly enhance the possibilities of many VE applications. In this paper we present a variation of the well-known ray-casting technique for fast and accurate selection of 2D widgets over a virtual window immersed into a 3D world. The main idea is to provide a new interaction mode where hand rotations are scaled down so that the ray is constrained to intersect the active virtual window. This is accomplished by changing the control-display ratio between the orientation of the user s hand and the ray used for selection. Our technique uses a curved representation of the ray providing visual feedback of the orientation of both the input device and the selection ray. The users feeling is that they control a flexible ray that gets curved as it moves over a virtual friction surface defined by the 2D window. We have implemented this technique and evaluated its effectiveness in terms of accuracy and performance. Our experiments on a four-sided CAVE indicate that the proposed technique can increase the speed and accuracy of component selection in 2D GUIs immersed into 3D worlds.
GA based Adaptive Sampling for Image-based Walkthrough
(The Eurographics Association, 2006) Lee, Dong Hoon; Kim, Jong Ryul; Jung, Soon Ki; Ming Lin and Roger Hubbold
This paper presents an adaptive sampling method for image-based walkthrough. Our goal is to select minimal sets from the initially dense sampled data set, while guaranteeing a visual correct view from any position in any direction in walkthrough space. For this purpose we formulate the covered region for sampling criteria and then regard the sampling problem as a set covering problem. We estimate the optimal set using Genetic algorithm, and show the efficiency of the proposed method with several experiments.
Wearable Mixed Reality System In Less Than 1 Pound
(The Eurographics Association, 2006) Peternier, Achille; Vexo, Frédéric; Thalmann, Daniel; Ming Lin and Roger Hubbold
We have designed a wearable Mixed Reality (MR) framework which allows to real-time render game-like 3D scenes on see-through head-mounted displays (see through HMDs) and to localize the user position within a known internet wireless area. Our equipment weights less than 1 Pound (0.45 Kilos). The information visualized on the mobile device could be sent on-demand from a remote server and realtime rendered onboard.We present our PDA-based platform as a valid alternative to use in wearable MR contexts under less mobility and encumbering constraints: our approach eliminates the typical backpack with a laptop, a GPS antenna and a heavy HMD usually required in this cases. A discussion about our results and user experiences with our approach using a handheld for 3D rendering is presented as well.

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