code: def buildDefaultRefWCS(self):
          
          self.default_refWCS = None
          if self.use_wcs:
              wcslist = []
              for scichip in self.chip_catalogs:
                  wcslist.append(self.chip_catalogs[scichip]['wcs'])
              self.default_refWCS = utils.output_wcs(wcslist)
docs: Generate a default reference WCS for this image.