anchor.diff:            & JJ(:,1), JJ(:,2), JJ(:,3))
   
         check_lines_all_heights: do k = 1,nh
  -        call checkline(maph, gth,                               &
  +        call checkray(maph, gth,                                &
                 & src(i,j) % lat, src(i,j) % lng, src(i,j) % h,   &
                 & lat,            lng,            hsct(k),        &
                 & JJ(k,4))
  
positive.code: 
    !-----------------------------------------------------------------------------
  
    pure subroutine checkline(maph, gth, lat1, lng1, h1, lat2, lng2, h2, attn)
      ! altitude map and geotransform
      real, dimension(:,:), intent(in) :: maph
      type(geotransform), intent(in) :: gth
  
negative.code:     Q(1:nn) = (h_ray(1:nn) * radearth - hterr(1:nn)) &
            & / (raylength * t(1:nn))
      attn = th(minval(Q(1:nn)) / real(0.001,fp))
    end subroutine checkray
  
    !-----------------------------------------------------------------------------
  
  