Spherical Harmonic Amplitudes From Grid Data
  The problem of resolving spherical harmonic components from numerical data defined on a rectangular grid has many applications, particularly for the problem of gravitational radiation extraction. A novel method due to Misner improves on traditional techniques by avoiding the need to cover the sphere with a coordinate system appropriate to the grid geometry. This paper will discuss Misner's method and suggest how it can be improved by exploiting local regression techniques. 
Mark E. Rupright