anchor.diff:      write(stderr,*)
   endif
   
  -write(stderr,*) 'Usage: perspective -viewer vx,vy,vz -look lx,ly,lz [-f IFILE] [-o OFILE]'
  +write(stderr,*) 'Usage: perspective -viewer vx,vy,vz -look lx,ly,lz [-scale S] [-f IFILE] [-o OFILE]'
   write(stderr,*)
  -write(stderr,*) '-viewer vx,vy,vz       Viewer position'
  -write(stderr,*) '-look lx,ly,lz         Look vector (from viewer to vanishing point)'
  +write(stderr,*) '-viewer VX,VY,VZ       Viewer position'
  +write(stderr,*) '-look LX,LY,LZ         Look vector (from viewer to center of view vanishing point)'
  +write(stderr,*) '-scale S               Scale output dimensions (default: 1.0)'
   write(stderr,*) '-f IFILE               Input file: x y z'
   write(stderr,*) '-o OFILE               Output file: projected x y'
   
  
positive.code:         nline = nline + 1
      endif
  
      ! Read input coordinates
      read (input_line,*,iostat=ios) x,y,z
      if (ios.ne.0) then
  
negative.code: double precision :: look_x
  double precision :: look_y
  double precision :: look_z
  
  double precision :: zoom_scale
  
  end module
  
  