This definition of x_dst ensure the following desirable property: for ??? ??? ?? = 0 , ??????????????????????????????????????????????????? ??? x_dst = 0 ; for ??? ??? ?? = ??_max , ?????????????????? ??? x_dst = f ??? tan ??? ( ??_max ) = w ??? / ??? 2 for ??? ??? ?? = ??_min , ????????????????????? ??? x_dst = f ??? tan ??? ( ??_min ) = - w ??? / ??? 2 i.e. x_dst is centered on the center of the