Abstract
This paper proposes the implementation of a framework for the development of collaborative extended reality (XR) applications. Using the framework, developers can focus on understanding which collaborative mechanisms they need to implement for the respective reality model application. In this paper we specifically study collaborative mechanisms around object manipulation in Virtual Reality (VR). As such, we planned a VR prototype using the proposed framework, which was used to validate the various interaction and collaboration features in VR. The gathered data from the user tests revealed that they enjoyed the experience and the collaborative mechanisms helped them work together. Furthermore, to understand whether the framework allowed for the development of XR applications, we decided to implement an augmented reality prototype as well. Afterwards, we ran an experiment with 4 VR and 3 AR users sharing the same virtual environment. The experiment was successful at allowing them to interact in real-time in the same shared environment. Therefore, the framework enables the development of XR applications that support different mixed-reality technologies.

Abstract
Typical VR interactions can be tiring, including standing up, walking, and mid-air gestures. Such interactions result in decreased comfort and session duration compared with traditional non-VR interfaces, which may, in turn, reduce productivity. Nevertheless, current approaches often neglect this aspect, making the VR experience not as promising as it can be. As we see it, desk VR experiences provide the convenience and comfort of a desktop experience and the benefits of VR immersion, being a good compromise between the overall experience and ergonomics. In this work, we explore navigation techniques targeted at desk VR users, using both controllers and a large multi-touch surface. We address travel and orientation techniques independently, considering only continuous approaches for travel as these are better suited for exploration and both continuous and discrete approaches for orientation. Results revealed advantages for a continuous controller-based travel method and a trend for a dragging-based orientation technique. Also, we identified possible trends towards task focus affecting overall cybersickness symptomatology.

Abstract

Abstract
Content generation is a heavy task in virtual worlds design. Procedural content generation techniques aim to agile this process by automating the 3D modelling with some degree of parametrisation. The novelty of this work is the procedural generation of the marine alga (Asparagopsis armata), taking into consideration the underwater environmental factors. The depth and the occlusion were the two parameters in this study to simulate how the alga growth is influenced by the environment where the alga grows. Starting by building a prototype to explore different L-systems categories to model the alga, the stochastic L-systems with parametric features were selected to generate different alga plasticities. Qualitative methods were used to evaluate the designed grammar and alga's animation results by comparing videos and images of the Asparagopsis armata with the computer-generated versions. © 2022 University of West Bohemia. All rights reserved.

Abstract
This paper presents a robust approach for 3D point reconstruction based on a set of images taken from a static scene with known. but not necessarily exact or regular, camera parameters. The points to be reconstructed are chosen from the contours of images, and a world-based formulation of the reconstruction problem and associated epipolar geometry is used. The result is a powerful mean of transparently integrating contributions from multiple images, and increased robustness to situations such as occlusions or apparent contours. Two steps for adding robustness are proposed: cross-checking, which validates a reconstructed point taken from an image by projecting it on a special subset of the remaining images; and merging, which fuses pairs of reconstructed points that are close in 3D space and that were initially chosen from different images. Results obtained with a synthetic scene (for ground truth comparison and error assessment), and two real scenes show the improved robustness achieved with the steps proposed.

Abstract
The urge to improve the life of older adults grows as this segment of society expands. Computers have an enormous potential to benefit the lives of older adults, however, the unawareness or disregard of their characteristics, renders technology, many times, impossible to use. Peripherals are a common obstacle when learning to operate computers, because the most common ones do not directly map the input in the user interface. It has been argued that touch- and gesture-based user interfaces, due to their direct mapping of input, can reduce the obstacles that older adults face, when using the computer. To assess this, this paper presents a project that uses a multi-touch tabletop system as a gaming platform for older adults. Specifically, it reports on the low-fidelity prototype that was built to test whether tangible objects can be used. Conclusions regarding the viability of tangible objects for that purpose are also drawn.