def first_intersection_point_in_voxel_space
      a_x_min = ax(@i_min)
      a_y_min = ay(@j_min)
      a_z_min = az(@k_min)
      a_x_max = ax(@i_max)
      a_y_max = ay(@j_max)
      a_z_max = az(@k_max)
      alpha_x = alpha_min_first_intersection([a_x_min, a_x_max])
      alpha_y = alpha_min_first_intersection([a_y_min, a_y_max])
      alpha_z = alpha_min_first_intersection([a_z_min, a_z_max])
      return alpha_x, alpha_y, alpha_z
    end
def first_intersection_point_in_voxel_space
      a_x_min = ax(@i_min)
      a_y_min = ay(@j_min)
      a_z_min = az(@k_min)
      a_x_max = ax(@i_max)
      a_y_max = ay(@j_max)
      a_z_max = az(@k_max)
      alpha_x = alpha_min_first_intersection([a_x_min, a_x_max])
      alpha_y = alpha_min_first_intersection([a_y_min, a_y_max])
      alpha_z = alpha_min_first_intersection([a_z_min, a_z_max])
      return alpha_x, alpha_y, alpha_z
    end
Determines the alpha values for the first intersection after
 the ray has entered the voxel space.

 @return [Array<Float>] directional x, y and z alpha values