make_line(
   start_point(make_line( $geometry,  make_point( LONGTO, LATTO))),
   centroid(
      offset_curve(
         make_line( $geometry,  make_point( LONGTO, LATTO)), 
         length(make_line( $geometry,  make_point( LONGTO, LATTO)))/+8.0
      )
   ),
   end_point(make_line( $geometry,  make_point( LONGTO, LATTO)))
)
