subroutine empty(en, x0, y0, z0, thx0, thy0, tx1, tx2,
     &     ty1, ty2, tz, enp, x, y, z, thx, thy)

      implicit none

      include 'const.inc'

      double precision en, x0, y0, z0, thx0, thy0, rx0, ry0, tx1, tx2
      double precision ty1, ty2, tz, x, y, z, thx, thy, rx, ry, ep, enp
      double precision xdis, ydis

c
      if((x0.ge.tx1.and.x0.le.tx2).and.(y0.ge.ty1.and.y0.le.ty2)) then

         xdis = x0 + tz*dtan(thx0)
         ydis = y0 + tz*dtan(thy0)

         if( (xdis.ge.tx1.and.xdis.le.tx2) .and.
     &        (ydis.ge.ty1.and.ydis.le.ty2) ) then
            x = xdis
            y = ydis
            z = z0 + tz
            thx = thx0
            thy = thy0
            enp = en
         else
            x = -1.d6
            y = -1.d6
            z = -1.d6
            thx = -1.d6
            thy = -1.d6
            enp = -1.d6
         endif
      else
         x = -1.d6
         y = -1.d6
         z = -1.d6
         thx = -1.d6
         thy = -1.d6
         enp = -1.d6
      endif

      return
      end