3D GUI implementation issues

One of the most important problems is proper GUI's location in virtual environment. The first possibility is to have GUI floating in the space [3] as other virtual objects. Anytime a user needs to change GUI's position, he must grab it and move to a new location. But a user can forget, where is 3D GUI situated and it means that he would spend too much time by searching for it in VE space. Useful enhancement is to limit GUI location so that it will be always situated in front of user view. This improvement will solve the problem when user loses knowledge about 3D GUI location, but on the other hand it shields view into scene. This disadvantage may be solved very simply by using some gesture with that we can show/hide GUI. But basically,there are many manners, how we may locate GUI and what gesture is more suitable for it's activation. The next problem is the selection of item in 3D GUI. This selection can be done using eg. 2D pointing, virtual touch (with visual feedback) or ray-casting technique (Figure 1). To confirm selection we can also use some gesture.

Figure 1: 3D menu - item selection with ray-casting technique.