code: def make_disk_kernel(radius, npix=501, cdelt=0.01, xpix=None, ypix=None):
      
  
      radius /= cdelt
  
      def fn(t, s): return 0.5 * (np.sign(s - t) + 1.0)
  
      dxy = make_pixel_distance(npix, xpix, ypix)
      k = fn(dxy, radius)
      k /= (np.sum(k) * np.radians(cdelt) ** 2)
  
      return k
docs: Make kernel for a 2D disk.
  
      Parameters
      ----------
  
      radius : float
        Disk radius in deg.