  Different ways of dealing with one-dimensional (1D) spectra, measured e.g. in
the Compton scattering or angular correlation of positron annihilation
radiation (ACAR) experiments are presented. On the example of divalent
hexagonal close packed metals it is shown what kind of information on the
electronic structure one can get from 1D profiles, interpreted in terms of
either 2D or 3D momentum densities. 2D and 3D densities are reconstructed from
merely two and seven 1D profiles, respectively. Applied reconstruction
techniques are particular solutions of the Radon transform in terms of
orthogonal Gegenabauer polynomials. We propose their modification connected
with so-called two-step reconstruction. The analysis is performed both in the
extended p and reduced k zone schemes. It is demonstrated that if positron wave
function or many-body effects are strongly momentum dependent, analysis of 2D
densities folded into k space may lead to wrong conclusions concerning the
Fermi surface. In the case of 2D ACAR data in Mg we found very strong many-body
effects. PACS numbers: 71.18.+y, 13.60.Fz, 87.59.Fm
