marker_set_UpdateSDF Subroutine

    impure subroutine marker_set_UpdateSDF(this,SDF)
      !> Updates the Surface Density Function.
      implicit none
      class(marker_set),    intent(inout) :: this                              !! A collection of tessellation elements
      type(eulerian_obj_r), intent(inout) :: SDF                               !! Surface Density Function
      ! work variables
      type(eulerian_obj_r):: tmp

      ! Initialize temporary field
      call tmp%Initialize('tmp',this%block,this%parallel,0)

      ! Filter particle surface area
      call this%Filter('SA',tmp)

      ! Add to total SDF
      SDF = SDF + tmp

      ! Clear data
      call tmp%Finalize()

      return
    end subroutine marker_set_UpdateSDF