Section: New Results

3D interactive techniques

Navigating in virtual environments with omnidirectional rendering

Participants : Jérôme Ardouin [contact] , Anatole Lécuyer [contact] , Maud Marchal.

The “FlyVIZ” enables humans to experience a real-time 360o vision of their surroundings for the first time. The visualization device combines a panoramic image acquisition system (positioned on top of the user's head) with a Head-Mounted Display (HMD). The omnidirectional images are transformed to fit the characteristics of HMD screens. As a result, the user can see his/her surroundings, in real-time, with 360o images mapped into the HMD field-of- view.

In order to safely simulate and evaluate our approach, we designed and evaluated [28] several visualization techniques, for navigating in virtual environments (VE). We have conducted an evaluation of different methods compared to a rendering method of reference, i.e. a perspective projection, in a basic navigation task. Our results confirm that using any omnidirectional rendering method could lead to more efficient navigation in terms of average task completion time. Among the different 360o projection methods, the subjective preference was significantly given to a cylindrical projection method (equirectangular). Taken together, our results suggest that omnidirectional rendering could be used in virtual reality applications in which fast navigation or full and rapid visual exploration are important. They pave the way to novel kinds of visual cues and visual rendering methods in virtual reality. This work was a collaboration with the Lagadic team (Inria Rennes).

Advances in locomotion interfaces for virtual environments

Participants : Anatole Lécuyer [contact] , Maud Marchal [contact] , Bruno Arnaldi.

Navigation, a fundamental task in Virtual Reality (VR), is greatly influenced by the locomotion interface being used, by the specificities of input and output devices, and by the way the virtual environment is represented. No matter how virtual walking is controlled, the generation of realistic virtual trajectories is absolutely required for some applications, especially those dedicated to the study of walking behaviors in VR, navigation through virtual places for architecture, rehabilitation and training.

First, we have studied the realism of unconstrained trajectories produced during virtual walking.We proposed a comprehensive evaluation framework consisting on a set of trajecto-graphical criteria and a locomotion model to generate reference trajectories [17] . We considered a simple locomotion task where users walk between two oriented points in space. The travel path was analyzed both geometrically and temporally in comparison to simulated reference trajectories. This work was a collaboration with the Mimetic team (Inria Rennes).

Secondly, we have introduced novel “Camera Motions” (CMs) to improve the sensations related to locomotion in virtual environments (VE) [27] . Traditional CMs are artificial oscillating motions applied to the subjective viewpoint when walking in the VE, and they are meant to evoke and reproduce the visual flow generated during a human walk. Our novel CMs are: (1) multistate, (2) personified, and (3) they can take into account the topography of the virtual terrain. In addition, they can then take into account avatar's fatigue and recuperation, and the topography for updating visual CMs accordingly. Taken together, our results suggest that our new CMs could be introduced in Desktop VR applications involving first-person navigation, in order to enhance sensations of walking, running, and sprinting, with potentially different avatars and over uneven terrains, such as for training, virtual visits or video games.

3D manipulation of virtual objects: 3-Point++

Participants : Thierry Duval [contact] , Thi Thuong Huyen Nguyen.

Manipulation in immersive Virtual Environments (VEs) is often difficult and inaccurate because humans have difficulty in performing precise positioning tasks or in keeping the hand motionless in a particular position without any help of external devices or haptic feedback. To address this problem, we proposed a set of four manipulation points attached to objects (called a 3-Point++ tool, including three handle points and their barycenter), by which users can control and adjust the position of objects precisely [40] . By determining the relative position between the 3-Point++ tool and the objects, and by defining different states of each manipulation point (called locked/unlocked or inactive/active), these points can be freely configured to be adaptable and flexible to enable users to manipulate objects of varying sizes in many kinds of positioning scenarios.

A survey of 3D object selection techniques for virtual environments

Participant : Ferran Argelaguet Sanz [contact] .

Computer graphics applications controlled through natural gestures are gaining increasing popularity these days due to recent developments in low-cost tracking systems and gesture recognition technologies. Although interaction techniques through naturalgestures have already demonstrated their benefits in manipulation, navigation and avatar-control tasks, effective selection with pointing gestures remains an open problem. We surveyed the state-of-the-art in 3D object selection techniques [13] . We reviewed important findings in human control models, analyze major factors influencing selection performance, and classify existing techniques according to a number of criteria. Unlike other components of the application's user interface, pointing techniques need a close coupling with the rendering pipeline, introducing new elements to be drawn, and potentially modifying the object layout and the way the scene is rendered. Conversely, selection performance is affected by rendering issues such as visual feedback, depth perception, and occlusion management. We thus reviewed existing literature paying special attention to those aspects in the boundary between computer graphics and human computer interaction.

Novel pseudo-haptic based interfaces

Participants : Pierre Gaucher, Ferran Argelaguet Sanz, Anatole Lécuyer [contact] , Maud Marchal.

Pseudo-haptics is a technique meant to simulate haptic sensations using visual feedback and properties of human visuo-haptic perception. In this course of action, we have extended its usage for gestural interfaces [33] and exploring its usage for the simulation of the local elasticity of images [14] .

Interacting with virtual objects through free-hand gestures do not allow users to perceive the physical properties of virtual objects. To provide enhanced interaction, we explored how the usage of a pseudo-haptic approach could be introduced while interacting with a 3D Carrousel [33] . In our approach, which is envisioned for showcasting purposes, virtual products are presented using a 3D carousel augmented with physical behavior and a pseudo-haptic effect aiming to attract the user to specific items. The user, through simple gestures, controls the rotation of the carousel, and can select, examine and manipulate the objects presented. Several demos can be tested on-line at Hybrid website .

Secondly, we have introduced the Elastic Images, a novel pseudo-haptic feedback technique which enables the perception of the local elasticity of images without the need of any haptic device [14] . The proposed approach focuses on whether visual feedback is able to induce a sensation of stiffness when the user interacts with an image using a standard mouse. The user, when clicking on a Elastic Image, is able to deform it locally according to its elastic properties. A psychophysical experiment was conducted to quantify this novel pseudo-haptic perception and determine its perceptual threshold (or its Just Noticeable Difference). The results showed that users were able to recognize up to eight different stiffness values with our method and confirmed that it provides a perceivable and exploitable sensation of elasticity.

Experiencing the past in virtual reality

Participant : Valérie Gouranton [contact] .

We designed a public experience and exhibition organized during the French National Days of Archaeology. This was the result of an interdisciplinary collaboration between archaeologists and computer scientists, centered on the immersive virtual reality platform Immersia, a node of the European Visionair project. This public exhibition had three main goals: (i) presenting our interdisciplinary collaboration, (ii) communicating on the scientific results of this collaboration, and (iii) offering an immersive experience in the past for visitors. In [34] we could present the scientific context of the event, its organization, and a discussion on feedbacks.

In the frame of the CNPAO project (section 8.1.3 ) we have also worked on the reconstitution of six archaeological sites located in the west of France ranging from prehistory to the Middle Ages: the Cairn of Carn Island, the covered pathway of Roh Coh Coet, the GohMin Ru megalithic site, the gallo-roman mansion of Vanesia, the keep of the Château de Sainte-Suzanne, the Porte des Champs of the Château d'Angers. Other proposals are currently under study [30] .

Perception of affordances in virtual reality

Participants : Anatole Lécuyer [contact] , Maud Marchal.

The perception of affordances could be a potential tool for sensorimotor assessment of physical presence, that is, the feeling of being physically located in a virtual place. We have evaluated the perception of affordances for standing on a virtual slanted surface [26] . Participants were asked to judge whether a virtual slanted surface supported up right stance. The objective was to evaluate if this perception was possible in virtual reality (VR) and comparable to previous works conducted in real environments. We found that the perception of affordances for standing on a slanted surface in virtual reality is possible and comparable (with an underestimation) to previous studies conducted in real environments. We also found that participants were able to extract and to use virtual information about friction in order to judge whether a slanted surface supported an upright stance. Finally, results revealed that the person's position on the slanted surface is involved in the perception of affordances for standing on virtual grounds. Taken together, our results show quantitatively that the perception of affordances can be effective in virtual environments, and influenced by both environmental and person properties. Such a perceptual evaluation of affordances in VR could guide VE designers to improve their designs and to better understand the effect of these designs on VE users.