s coarseness (Srinivasan and Basdogan, 1997). Synthetic textures such as wood, sandpaper, cobblestone, rubber, and plastic may also be created using mathematical functions for the height field (Anderson, 1996; Basogan, Ho, and Srinivasan, 1997). The ENCHANTER environment (Jansson, Faenger , Konig and Billberger, 1998) has a texture mapper which can render sinus, triangular, and rectangular textures as well as textures provided by other programs, for any haptic object provided by the Ghost SDK.Issues in haptic renderingResearchers working with force feedback devices for object sensing have been concerned with issues of presence, or the fidelity (realism) of the haptic experience. For instance, Brown and Colgate (1994), in their physics-based approach to haptic display, address the issue of stability guarantees in virtual environments. In particular they note the threat to presence created when the virtual environment becomes computationally unstable, as for example when a normally "passive" tool, such as a chisel, begins to move independently of the control of the user who is wielding it. Similarly, a virtual wall must unilaterally constrain the user's forward movement. Brown and Colgate develop a model for improving the passivity of the haptic display through inherent physical damping and the impedence of virtual walls through increased sampling (update rates). The many potential applications in industry, the military, and entertainment for force feedback in multi-user environments, where two or more users orient to and manipulate objects in a shared environment, have led to work such as that of Buttolo and his colleagues (Buttolo, Hewitt, Oboe, & Hannaford, 1997; Buttolo, Oboe, Hannaford, & McNally, 1996), who note that the addition of force feedback to multi-user environments demands low latency and high collision detection sampling rates. LANs, because of their low communication delay, may be conducive to applications in which users ...
