var arr_s2 = [],
    arr_s = [],
    colour_positions = [],
    colour_values = [],
    thickness_positions = [],
    thickness_values = [],
    //change the values of the following five variables to change the grid size
//change the values of the following five variables to change the grid size
    x_limit_1 = -10,
    x_limit_2 = 10,
    y_limit_1 = 5,
    y_limit_2 = 30,
    z = -4, //perpendicular distance of the grid from the XY plane
    sc = 100,
    x_inc = 5,
    y_inc = 5,
    z_inc = 5,