Data items in the EM_MAP_EIGENVALUES category record details
about values of the eigenvectors for projection sets.
2d projection images are considered as a linear combination of
the main eigenvectors 'eigenimages' of the projection set,
enabling a reduction of the total amount of data and simplifying
its interpretation. The eigenvalue spectrum gives an indication
of the randomness of the data that is included in the reconstruction.
The completeness of the data can be verified eg all eigenvalues exceeded 1.0.