The GUI is implemented as follows: on the graphic loaded in the
graphics viewer, users can click the right mouse key to activate
the tool page. A total of 8 tool balls are aligned in a circle around the
center (101), and each tool icon has a circular active area with
radius of 16 pixels (102). These tool balls are evenly distributed in
a circle with radius of 70 pixels (103) (Fig. 6, left). When the mouse