Plasma can be studied and characterised by the analysis of its radiation. Signals obtained by passive spectroscopy contain much information about temperature, density and flux of the main species and impurities. The interpretation of measured line intensities requires the knowledge of atomic physics describing the specific radiation from the plasma. Tomographic methods are applied but they need symmetries for the calculation of local parameters. Additionally in magnetic confined plasmas the interpretation might be more difficult due to the Zeeman splitting.