Radial abundance gradients from planetary nebulae at different distances
  from the galactic plane
  We investigate the variations of the radial O/H abundance gradients from
planetary nebulae (PN) located at different distances from the galactic plane.
In particular, we determine the abundance gradients at different heights from
the plane in order to investigate a possible gradient inversion for the objects
at larger distances from the plane. We consider a large sample of PN with known
distances, so that the height relative to the galactic plane can be derived,
and accurate abundances, so that the gradients can be determined.
