Download the survey footprint for HEALpix pixels.

def footprint(self,nside):
        """
        Download the survey footprint for HEALpix pixels.
        """
        import healpy
        import ugali.utils.projector
        if nside > 2**9: raise Exception("Overflow error: nside must be <=2**9")
        pix = np.arange(healpy.nside2npix(nside),dtype='int')
        footprint = np.zeros(healpy.nside2npix(nside),dtype='bool')
        ra,dec = ugali.utils.projector.pixToAng(nside,pix)
        table_name = 'Pix%i'%nside
        self.upload(np.array([pix,ra,dec]).T, ['pix','ra','dec'], name=table_name)
        radius = healpy.nside2resol(nside_superpix,arcmin=True)

        query="""
        SELECT t.pix, dbo.fInFootprintEq(t.ra, t.dec, %g)
        FROM %s AS t
        """%(radius, table_name)