  Computing spherical harmonic decompositions is a ubiquitous technique that
arises in a wide variety of disciplines and a large number of scientific codes.
Because spherical harmonics are defined by integrals over spheres, however, one
must perform some sort of interpolation in order to compute them when data is
stored on a cubic lattice. Misner (2004, Class. Quant. Grav., 21, S243)
presented a novel algorithm for computing the spherical harmonic components of
data represented on a cubic grid, which has been found in real applications to
be both efficient and robust to the presence of mesh refinement boundaries. At
the same time, however, practical applications of the algorithm require
knowledge of how the truncation errors of the algorithm depend on the various
parameters in the algorithm. Based on analytic arguments and experience using
the algorithm in real numerical simulations, I explore these dependencies and
provide a rule of thumb for choosing the parameters based on the truncation
errors of the underlying data. I also demonstrate that symmetries in the
spherical harmonics themselves allow for an even more efficient implementation
of the algorithm than was suggested by Misner in his original paper.
