code: def restoreWCS(self,prepend=None):
          
          # Open header for image
          image = self.rootname
  
          if prepend: _prepend = prepend
          elif self.prepend: _prepend = self.prepend
          else: _prepend = None
  
          # Open image as writable FITS object
          fimg = fileutil.openImage(image, mode='update')
          # extract the extension ID being updated
          _root,_iextn = fileutil.parseFilename(self.rootname)
          _extn = fileutil.getExtn(fimg,_iextn)
  
          if len(self.backup) > 0:
              # If it knows about the backup keywords already,
              # use this to restore the original values to the original keywords
              for newkey in self.revert.keys():
                  if newkey != 'opscale':
                      _orig_key = self.revert[newkey]
                      _extn.header[_orig_key] = _extn.header[newkey]
          elif _prepend:
              for key in self.wcstrans.keys():
                  # Get new keyword name based on old keyname
                  #    and prepend string
                  if key != 'pixel scale':
                      _okey = self._buildNewKeyname(key,_prepend)
  
                      if _okey in _extn.header:
                          _extn.header[key] = _extn.header[_okey]
                      else:
                          print('No original WCS values found. Exiting...')
                          break
          else:
              print('No original WCS values found. Exiting...')
  
          fimg.close()
          del fimg
docs: Resets the WCS values to the original values stored in
              the backup keywords recorded in self.backup.