The yellow green and red axis controls are positioned at 0,0,0. The axis is left in for perspective for the position of the perpendicular line. The 2 red points P1, P2 are is the line that you want to create a perpendicular extension to. The yellow point between P1, & P2 is the center point. The center point connects with the second yellow point to make the perpendicular point. Notice that the perpendicular line is plotted at irregular points, not something you could normally draw without calculating.