docs: def supplement(self,coordsys='gal'):
          """ Add some supplemental columns """
          from ugali.utils.projector import gal2cel, gal2cel_angle
          from ugali.utils.projector import cel2gal, cel2gal_angle
  
          coordsys = coordsys.lower()
          kwargs = dict(usemask=False, asrecarray=True)
          out = copy.deepcopy(self)
  
          if ('lon' in out.names) and ('lat' in out.names):
              # Ignore entries that are all zero
              zeros = np.all(self.ndarray==0,axis=1)
  
              if coordsys == 'gal':
                  ra,dec = gal2cel(out.lon,out.lat)
                  glon,glat = out.lon,out.lat
              else:
                  ra,dec = out.lon,out.lat
                  glon,glat = cel2gal(out.lon,out.lat)
  
              ra[zeros] = 0; dec[zeros] = 0
              glon[zeros] = 0; glat[zeros] = 0
  
              names = ['ra','dec','glon','glat']
              arrs = [ra,dec,glon,glat]
              out = mlab.rec_append_fields(out,names,arrs).view(Samples)
              #out = recfuncs.append_fields(out,names,arrs,**kwargs).view(Samples)
  
              if 'position_angle' in out.names:
                  if coordsys == 'gal':
                      pa_gal = out.position_angle
                      pa_cel = gal2cel_angle(out.lon,out.lat,out.position_angle)
                      pa_cel = pa_cel - 180.*(pa_cel > 180.)
                  else:
                      pa_gal = cel2gal_angle(out.lon,out.lat,out.position_angle)
                      pa_cel = out.position_angle
                      pa_gal = pa_gal - 180.*(pa_gal > 180.)
                      
                  pa_gal[zeros] = 0; pa_cel[zeros] = 0
                  names = ['position_angle_gal','position_angle_cel']
                  arrs = [pa_gal,pa_cel]
                  out = recfuncs.append_fields(out,names,arrs,**kwargs).view(Samples)
          
          return out