Two-handed haptic feedback in generic virtual environments

Since [years] we hear about Virtual Reality as a discipline that could potentially provide benefits to many applications. Basically, the principle of Virtual Reality consists in stimulating user senses in order to give the impression to be in another place which they can discover and interact with. Today, most virtual reality systems create realistic visual and auditive environments. However the interaction with these environments can not be considered as natural. Indeed, we often use devices such as mouse, keyboard or joystick to move or manipulate them. These paradigms of interaction are in fact metaphors, which are not similar to reality. In some situations they are practical and efficient. However, the lack of intuitiveness sometimes makes them limited or simply ineffective. To overcome this, researchers can use Haptic Devices. They are designed to simulate what is commonly called the "sense of touch", which includes more specifically, tactile, pain sense, thermal sense, and proprioception. Proprioception is knowledge gained by the perception of the relative member's position of the human body. In this thesis, we particularly focus on the simulation of proprioception. There are two advantages of such haptic devices. First, they can give the user more information on the nature of virtual objects (size, weight, finish, rigidity, etc.). Second, they can provide interaction paradigms that are closer to reality (three-dimensional interaction in a three-dimensional world). However, haptic device mechanics is complex. Moreover, proprioception is a sense that covers the entire body which is a rather large surface. For this reason, haptic devices usually apply force feedback on a very small portion of the body, such as fingertip. In addition to this hardware constraint, haptic research also faces software constraints. Indeed, a haptic application requires many computer resources in order to perform collision detection, dynamic animation of objects, and force feedback computation. Moreover, this should be done at a refresh rate that is much higher than the visualization for producing a convincing result. In the first part of this thesis, we propose to increase realism and complexity of haptic applications. To achieve this goal, we use a state-of-the-art commercial device which allows to acquire the posture and position of both hands, and to apply forces on the fingertips and wrists. We propose techniques to calibrate and improve the comfort of these kinds of devices in order to integrate them into Virtual Environments. However, a two-handed haptic device do not presents only advantages. Indeed, It is much more complicated to compute forces on two hand models, than on a single point or fingertip. For this reason, in this thesis, we propose a framework to optimize this computation. Thanks to it, we can create Virtual Environments in which an object is graspable and dynamically animated by the laws of physics. When the object is seized by both hands, the