#define WITH_PAINT 0
   
      subroutine define_geometry()
      real fiber_length
      real fiber_width(3)
      real fiber_pitch

      character*20 natmed
      integer nmat
      integer isvol
      integer ifield
      real fieldm
      real tmaxfd
      real stemax
      real deemax
      real epsil
      real stmin
      real ubuf(9)
      integer nwbuf
       
      integer npckov
      real ppckov(2)
      real absco(2)
      real effic(2)
      real rindex(2)

      character*4 chname
      character*4 chshape
      integer nmed
      real par(9)
      integer npar
      integer ivolu
      
      integer nr
      character*4 chmoth
      real x,y,z
      integer irot
      character*4 chonly

c define the geometry dimensions
      fiber_width(1) = 0.176
      fiber_width(2) = 0.192
      fiber_width(3) = 0.200
      fiber_length = 2.0
      fiber_pitch = 0.22

c define the tracking media
      isvol = 0
      ifield = 0
      fieldm = 0
      tmaxfd = 0
      stemax = 0
      deemax = 0
      epsil = 1e-5
      stmin = 1e-5
      nwbuf = 0
      nmed = 1
      natmed = 'atmosphere medium'
      nmat = 15 ! air
      call gstmed(nmed,natmed,nmat,isvol,ifield,fieldm,tmaxfd,stemax,
     +            deemax,epsil,stmin,ubuf,nwbuf)
      nmed = 100
      natmed = 'fiber core medium'
      nmat = 100
      call gstmed(nmed,natmed,nmat,isvol,ifield,fieldm,tmaxfd,stemax,
     +            deemax,epsil,stmin,ubuf,nwbuf)
      nmed = 101
      natmed = 'inner clad medium'
      nmat = 101
      call gstmed(nmed,natmed,nmat,isvol,ifield,fieldm,tmaxfd,stemax,
     +            deemax,epsil,stmin,ubuf,nwbuf)
      nmed = 102
      natmed = 'outer clad medium'
      nmat = 102
      call gstmed(nmed,natmed,nmat,isvol,ifield,fieldm,tmaxfd,stemax,
     +            deemax,epsil,stmin,ubuf,nwbuf)

c assign the refractive properties of these media
      nmed = 1
      npckov = 2
      ppckov(1) = 1e-9
      ppckov(2) = 4e-9
      absco(1) = 1e6
      absco(2) = 1e6
      effic(1) = 0
      effic(2) = 0
#if WITH_PAINT
      rindex(1) = 2.5
      rindex(2) = 2.5
#else
      rindex(1) = 1
      rindex(2) = 1
#endif
      call gsckov(nmed,npckov,ppckov,absco,effic,rindex)
      nmed = 100
      rindex(1) = 1.60
      rindex(2) = 1.60
      call gsckov(nmed,npckov,ppckov,absco,effic,rindex)
      nmed = 101
      rindex(1) = 1.49
      rindex(2) = 1.49
      call gsckov(nmed,npckov,ppckov,absco,effic,rindex)
      nmed = 102
      rindex(1) = 1.42
      rindex(2) = 1.42
      call gsckov(nmed,npckov,ppckov,absco,effic,rindex)
      
c define the world box
      nmed = 1
      chname = 'SITE'
      chshape = 'BOX'
      par(1) = 100.
      par(2) = 100.
      par(3) = 100.
      npar = 3
      call gsvolu(chname,chshape,nmed,par,npar,ivolu)

c define the scintillating fiber segment
      nmed = 100
      chname = 'CORE'
      chshape = 'BOX'
      par(1) = fiber_length/2
      par(2) = fiber_width(1)/2
      par(3) = fiber_width(1)/2
      npar = 3
      call gsvolu(chname,chshape,nmed,par,npar,ivolu)
      nmed = 101
      chname = 'CLA1'
      chshape = 'BOX'
      par(1) = fiber_length/2
      par(2) = fiber_width(2)/2
      par(3) = fiber_width(2)/2
      npar = 3
      call gsvolu(chname,chshape,nmed,par,npar,ivolu)
      nmed = 102
      chname = 'CLA2'
      chshape = 'BOX'
      par(1) = fiber_length/2
      par(2) = fiber_width(3)/2
      par(3) = fiber_width(3)/2
      npar = 3
      call gsvolu(chname,chshape,nmed,par,npar,ivolu)

c place the components of the fiber segment inside each other
      chname = 'CORE'
      chmoth = 'CLA1'
      nr = 1
      x = 0
      y = 0
      z = 0
      irot = 0
      chonly = 'ONLY'
      call gspos(chname,nr,chmoth,x,y,z,irot,chonly)
      chname = 'CLA1'
      chmoth = 'CLA2'
      nr = 1
      x = 0
      y = 0
      z = 0
      irot = 0
      chonly = 'ONLY'
      call gspos(chname,nr,chmoth,x,y,z,irot,chonly)

c place 15 copies of the fibers in a 3x5 configuration in the mother volume
      chname = 'CLA2'
      chmoth = 'SITE'
      nr = 0
      do i=-1,1
        do j=-2,2
          nr = nr + 1
          x = 0
          y = j*fiber_pitch
          z = i*fiber_pitch
          irot = 0
          chonly = 'ONLY'
          call gspos(chname,nr,chmoth,x,y,z,irot,chonly)
        enddo
      enddo
      end

      real function guplsh(medi0,medi1)
      integer medi0,medi1
      if (medi0 .eq. 102 .and. medi1 .eq. 1) then
#if WITH_PAINT
        guplsh = 0.
#else
        guplsh = 1.
#endif
      else
        guplsh = 1.
      endif
      end