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GRAPP 2006 Special Issue

3.2006, 4


View-Dependent Extraction of Contours with Distance Transforms
for Adaptive Polygonal Mesh Simplification

GRAPP 2006 Special Issue

Susana Mata et al.

During decades Distance Transforms have proven to be useful for many image processing applications, and more recently, they have started to be used in computer graphics environments. The goal of this paper is to propose a new technique based on Distance Transforms for detecting mesh elements which are close to the objects' external contour (from a given point of view), and using this information for weighting the approximation error which will be tolerated during the mesh simplification process. The obtained results are evaluated in two ways: visually and using an objective metric that measures the geometrical difference between two polygonal meshes.

[Submitted: June 30th, 2006 | In Peer-Review: July 3rd, 2006 | Accepted: August 14th, 2006 | Resubmitted: December 5th, 2006 | Published: February 7th, 2007 ]

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3.2006, 5


Exploring Urban Environments Using Virtual and Augmented Reality

GRAPP 2006 Special Issue

Fotis Liarokapis et al.

In this paper, we propose the use of specific system architecture, based on mobile device, for navigation in urban environments. The aim of this work is to assess how virtual and augmented reality interface paradigms can provide enhanced location based services using real-time techniques in the context of these two different technologies. The virtual reality interface is based on faithful graphical representation of the localities of interest, coupled with sensory information on the location and orientation of the user, while the augmented reality interface uses computer vision techniques to capture patterns from the real environment and overlay additional way-finding information, aligned with real imagery, in real-time. The knowledge obtained from the evaluation of the virtual reality navigational experience has been used to inform the design of the augmented reality interface. Initial results of the user testing of the experimental augmented reality system for navigation are presented.

[Submitted: July 3rd, 2006 | In Peer-Review: July 27th, 2006 | Accepted: September 25th, 2006 | Resubmitted: December 12th, 2006 | Published: February 6th, 2007 ]

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3.2006, 7


System Architecture of a Mixed Reality Framework

GRAPP 2006 Special Issue

Helmut Seibert and Patrick Dähne

In this paper the software architecture of a framework which simplifies the development of applications in the area of Virtual and Augmented Reality is presented. It is based on VRML/X3D to enable rendering of audio-visual information. We extended our VRML rendering system by a device management system that is based on the concept of a data-flow graph. The aim of the system is to create Mixed Reality (MR) applications simply by plugging together small prefabricated software components, instead of compiling monolithic C++ applications. The flexibility and the advantages of the presented framework are explained on the basis of an exemplary implementation of a classic Augmented Realityapplication and its extension to a collaborative remote expert scenario.

[Submitted: July 24th, 2006 | In Peer-Review: August 8th, 2006 | Accepted: November 23rd, 2006 | Resubmitted: January 18th, 2007 | Published: May 16th, 2007 ]

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3.2006, 10


Lag Camera: A Moving Multi-Camera Array for Scene-Acquisition

GRAPP 2006 Special Issue

Daniel Aliaga et al.

Many applications, such as telepresence, virtual reality, and interactive walkthroughs, require a three-dimensional (3D)model of real-world environments. Methods, such as lightfields, geometric reconstruction and computer vision use cameras to acquire visual samples of the environment and construct a model. Unfortunately, obtaining models of real-world locations is a challenging task. In particular, important environments are often actively in use, containing moving objects, such as people entering and leaving the scene. The methods previously listed have difficulty in capturing the color and structure of the environment while in the presence of moving and temporary occluders. We describe a class of cameras called lag cameras. The main concept is to generalize a camera to take samples over space and time. Such a camera, can easily and interactively detect moving objects while continuously moving through the environment. Moreover, since both the lag camera and occluder are moving, the scene behind the occluder is captured by the lag camera even from viewpoints where the occluder lies in between the lag camera and the hidden scene. We demonstrate an implementation of a lag camera, complete with analysis and captured environments.

[Submitted: June 26th, 2006 | In Peer-Review: July 27th, 2006 | Accepted: December 13th, 2006 | Resubmitted: January 30th, 2007 | Published: April 17th, 2007 ]

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3.2006, 12


High level methods for scene exploration

GRAPP 2006 Special Issue

Dmitry Sokolov et al.

Virtual worlds exploration techniques are used in a wide variety of domains — from graph drawing to robot motion. This paper is dedicated to virtual world exploration techniques which have to help a human being to understand a 3D scene. An improved method of viewpoint quality estimation is presented in the paper, together with a new off-line method for automatic 3D scene exploration, based on a virtual camera. The automatic exploration method is working in two steps. In the first step, a set of “good” viewpoints is computed. The second step uses this set of points of view to compute a camera path around the scene. Finally, we define a notion of semantic distance between objects of the scene to improve the approach.

[Submitted: June 26th, 2006 | In Peer-Review: June 27th, 2006 | Accepted: January 2nd, 2007 | Published: October 12th, 2007]

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