Check valid parameter range and download isochrones from:
        http://stev.oapd.inaf.it/cgi-bin/cmd

def download(self,age=None,metallicity=None,outdir=None,force=False):
        """
        Check valid parameter range and download isochrones from:
        http://stev.oapd.inaf.it/cgi-bin/cmd
        """
        try:
            from urllib.error import URLError
        except ImportError:
            from urllib2 import URLError

        if age is None: age = float(self.age)
        if metallicity is None: metallicity = float(self.metallicity)

        if outdir is None: outdir = './'
        basename = self.params2filename(age,metallicity)
        outfile = os.path.join(outdir,basename)
            
        if os.path.exists(outfile) and not force:
            try:
                self.verify(outfile,self.survey,age,metallicity)
                logger.info("Found %s; skipping..."%(outfile))
                return
            except Exception as e:
                msg = "Overwriting corrupted %s..."%(outfile)
                logger.warn(msg)
                os.remove(outfile)
                
        mkdir(outdir)

        self.print_info(age,metallicity)
        self.query_server(outfile,age,metallicity)

        if not os.path.exists(outfile):
            raise RuntimeError('Download failed')

        try:
            self.verify(outfile,self.survey,age,metallicity)
        except Exception as e:
            msg = "Output file is corrupted."
            logger.error(msg)
            msg = "Removing %s."%outfile
            logger.info(msg)
            os.remove(outfile)
            raise(e)

        return outfile