  Basis functions which are invariant under the operations of a rotational
point group $G$ are able to describe any 3-D object which exhibits the
rotational point group symmetry. However, in order to characterize the spatial
statistics of an ensemble of objects in which each object is different but the
statistics exhibit the symmetry, a complete set of basis functions is required.
In particular, for each irreducible representation (irrep) of $G$, it is
necessary to include basis functions that transform according to that irrep.
This complete set of basis functions is a basis for square-integrable functions
on the surface of the sphere in 3-D. Because the objects are real-valued, it is
convenient to have real-valued basis functions. In this paper, the existence of
such real-valued bases is proven and an algorithm for their computation is
provided for the icosahedral $I$ and the octahedral $O$ symmetries.
Furthermore, it is proven that such a real-valued basis does not exist for the
tetrahedral $T$ symmetry because some irreps of $T$ are essentially complex.
The importance of these basis functions to computations in single-particle
cryo-electron microscopy is described.
