program ReadEnvi
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
c
c                      R E A D E N V I
c
c  Reads Envisat SGDR data 
c  Input:
c         ENVISAT file name
c         outfile
c
c 
c  output in gravsoft format with average h,hmin/geoid,avruf
c  ldos must be set false for unix systems 
c
c  (c) Henriette Skourup, Danish National Space Center, Feb 2006
c
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
      implicit double precision(a-h,o-z)
      double precision lat,lon	
      character*72 ifile,ofile
      integer*1 b(6769253)
      integer recno,irec,count,mdsl,j0
      logical ldos
      common /rec/ b,ldos

      integer*4 int_four
      integer*2 d(2)
      equivalence(int_four,d)	

      read(*,*) ifile	
      read(*,*) ofile	
      read(*,*) tjd1,tjd2,rlat1,rlat2,rlon1,rlon2
      write(*,*) 'READENVI ',ifile
      open(10,file=ifile,access='direct',form='unformatted',
     .recl=6769253)
      open(20,file=ofile,status='unknown')
 
c ldos: true for windows, reverse byte order
c
      ldos = .true.

      irec=18425
      mdsl=2492
      recno=25
      count=1

10    if (irec.lt.6769253) then
        read(10,rec=1,err=80) b
        rlat = i4(16+irec)*1.d-6
        rlon = i4(20+irec)*1.d-6

        j0=0
	do j=1,20
	  k1 = i2(1308+irec+j0)
	  dlat = ineg(k1)*1.d-5
	  lat = rlat + dlat
	  k2 = i2(1348+irec+j0)
	  dlon = ineg(k2)*1.d-5
	  lon = rlon + dlon
c  output all recs
          write(20,20) lat,lon
20        format(f12.7,f13.7)
	  j0=j0+2
	end do

c	write(*,*) count,rlat,rlon,dlat,dlon
        count=count+1
        irec=irec+mdsl
        goto 10
      else 
        goto 80
      end if

80    continue
      close(10)	
      close(20)	
      end


cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
      integer*4 function i4(i0)
c     ---------------------------
c     reads integer*4 at adress i0     
c
      integer*1 b(6769253),b1(4)
      logical ldos
      equivalence(b1,k)
      common /rec/ b,ldos
      if (ldos) then
        b1(4) = b(i0+1)
        b1(3) = b(i0+2)
        b1(2) = b(i0+3)
        b1(1) = b(i0+4)
      else 
        b1(1) = b(i0+1)
        b1(2) = b(i0+2)
        b1(3) = b(i0+3)
        b1(4) = b(i0+4)
      endif
      i4 = k
      return
      end      
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
      integer*2 function i2(i0)
c     ---------------------------
c     reads integer*4 at adress i0     
c
      integer*1 b(6769253),b1(2)
      logical ldos
      equivalence(b1,k)
      common /rec/ b,ldos
      if (ldos) then
        b1(2) = b(i0+1)
        b1(1) = b(i0+2)
      else 
        b1(1) = b(i0+1)
        b1(2) = b(i0+2)
      endif
      i2 = k
      return
      end      
cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
      integer*4 function ineg(k)
c     ---------------------------
c  reads integer*4 at adress i0     
c
      integer*4 int_four
      integer*2 d(2)
      equivalence(int_four,d)	
      d(1) = k	
      d(2) = 0
      if (int_four.gt.32767) then
	ineg = int_four - 65536
      else
	ineg = int_four
      endif
      return
      end