3-D ionization structure (in stereoscopic view) of planetary nebulae: the case of NGC 1501 R. Ragazzoni, E. Cappellaro, S. Benetti, M. Turatto and F. Sabbadin A&A, 369 3 (2001) 1088-1103 Published online: 15 April 2001 DOI: 10.1051/0004-6361:20010229