There are two trackers, one for each hand. In SFA, as with other MR applications, interaction tasks are split amongst the hands based on required level of control. As mentioned above, the trackers support a form of menuing to control state oriented items as well as function activation. This is accomplished using a technique called sundial menus . Sundials are described in more detail here .
Subsets are cubic volumes in the three-dimensional scene created by the user.
If any subsets exist, glyphs lying outside the subsets never get drawn. If a single subset exists, only glyphs within that subset get drawn. The nose button on the DH tracker has been reserved for subsetting functionality. While holding the nose button down, movement of the tracker moves the position of the second defining vertex. This movement continues until the user releases the nose button, at which time the subset is saved, and the list of glyphs to be drawn is recalculated.