pro show
  window,xsize=500,ysize=500
  FOR i=0L,100 DO BEGIN
     snr=string(i,form='(i03)')
     readnew,'snap_'+snr,x,'POS'
     plot,x[0,*],x[1,*],psym=4,xr=[-12000,12000],yr=[-12000,12000],xst=1,yst=1
     save_screen,'frame_'+snr
  END
     
end