NFSFT - nonequispaced fast spherical Fourier transform

Fourier analysis on the sphere has, despite other fields, practical relevance in tomography, geophysics, seismology, meteorology and crystallography. In analogy to the complex exponentials $\mathrm{e}^{\mathrm{i} k x}$ on the torus, the spherical harmonics form the orthogonal Fourier basis with respect to the usual inner product on the sphere.