  Physical systems with symmetries are described by functions containing
kinematical and dynamical parts. We consider the case when kinematical
symmetries are described by a noncompact semisimple real Lie group $G$. Then
separation of kinematical parts in the functions is fulfilled by means of
harmonic analysis related to the group $G$. This separation depends on choice
of a coordinate system on the space where a physical system exists. In the
paper we review how coordinate systems can be chosen and how the corresponding
harmonic analysis can be done. In the first part we consider in detail the case
when $G$ is the de Sitter group $SO_0(1,4)$. In the second part we show how the
corresponding theory can be developed for any noncompact semisimple real Lie
group.
