Abstract
Current immersive modeling environments use non-natural tools and interfaces to support traditional shape manipulation operations. In the future, we expect the availability of natural methods of interaction with 3D models in immersive environments to become increasingly important in several industrial applications. In this paper, we present a study conducted on a group of potential users with the aim of verifying if there is a common strategy in gestural and vocal interaction in immersive environments when the objective is modifying a 3D shape model. The results indicate that users adopt different strategies to perform the different tasks but in the execution of a specific activity it is possible to identify a set of similar and recurrent gestures. In general, the gestures made are physically plausible. During the experiment, the vocal interaction was used quite rarely and never to express a command to the system but rather to better specify what the user was doing with gestures.

Abstract
Virtual Reality (VR) is again in the spotlight. However, interactions and modeling operations are still major hurdles to its complete success. To make VR Interaction viable, many have proposed mid-air techniques because of their naturalness and resemblance to physical world operations. Still, natural mid-air metaphors for Constructive Solid Geometry (CSG) are still elusive. This is unfortunate, because CSG is a powerful enabler for more complex modeling tasks, allowing to create complex objects from simple ones via Boolean operations. Moreover, Head-Mounted Displays occlude the real self, and make it difficult for users to be aware of their relationship to the virtual environment. In this paper we propose two new techniques to achieve Boolean operations between two objects in VR. One is based on direct-manipulation via gestures while the other uses menus. We conducted a preliminary evaluation of these techniques. Due to tracking limitations, results allowed no significant conclusions to be drawn. To account for self-representation, we compared full-body avatar against an iconic cursor depiction of users' hands. In this matter, the simplified hands-only representation improved efficiency in CSG modelling tasks. © 2017 IEEE.

Abstract
Selecting objects outside user's arm-reach in Virtual Reality still poses significant challenges. Techniques proposed to overcome such limitations often follow arm-extension metaphors or favor the use of selection volumes combined with ray-casting. Nonetheless, these approaches work for room sized and sparse environments, and they do not scale to larger scenarios with many objects. We introduce PRECIOUS, a novel mid-air technique for selecting out-of-reach objects. It employs an iterative progressive refinement, using cone-casting to select multiple objects and moving users closer to them in each step, allowing accurate selections. A user evaluation showed that PRECIOUS compares favorably against existing approaches, being the most versatile. © 2017 IEEE.

Abstract
Stereoscopic tabletops offer unique visualization capabilities, enabling users to perceive virtual objects as if they were lying above the surface. While allowing virtual objects to coexist with user actions in the physical world, interaction with these virtual objects above the surface presents interesting challenges. In this paper, we aim to understand which approaches to 3D virtual object manipulations are suited to this scenario. To this end, we implemented five different techniques based on the literature. Four are mid-air techniques, while the remainder relies on multi-touch gestures, which act as a baseline. Our setup combines affordable non-intrusive tracking technologies with a multi-touch stereo tabletop, providing head and hands tracking, to improve both depth perception and seamless interactions above the table. We conducted a user evaluation to find out which technique appealed most to participants. Results suggest that mid-air interactions, combining direct manipulation with six degrees of freedom for the dominant hand, are both more satisfying and efficient than the alternatives tested.

Abstract
The number and size of 3D object repositories have been increasing at a considerable rate. Consequently, finding a specific 3D model in such collections is getting more difficult. Current 3D search engines do not take advantage of novel interaction technologies, usually presenting query results in grids of thumbnails. This greatly hinders objects' interpretation and allows little to none manipulation at all. Immersive environments are believed as promising solutions for displaying 3D models, allowing complete representations of the models. These environments can be enhanced with multimodal techniques for a more natural interaction. In this paper we present a prototype that uses immersive visualization and mid-air interactions to explore query results in a dataset with 3D objects, using one of four different visualization modes. We evaluated these modes with 29 users and concluded that our immersive approaches are preferred by users and, albeit novel, perform at par relatively to traditional bi-dimensional grids with thumbnails.

Abstract
Manipulating objects is an essential aspect in virtual environments. Nonetheless, object positioning in immersive virtual environments relying in direct and natural approaches is still difficult. Previous research concluded that degrees-of-freedom separation in mouse and touch interfaces led to positive results. In this document we present a user evaluation to assess if explicit separation of degrees-of-freedom also benefits mid-air manipulation tasks. We implemented a virtual widget based technique that allows users to control a single DOF, and compared it against a direct approach and the PRISM technique, which adjusts the ratio between the hand and object movement. The results of our assessment suggest that full DOF separation benefits precision in spatial manipulations, at the expense of additional time for complex tasks. From these results we proposed a new technique that combines different aspects from the three techniques compared in our assessment.