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Spherical harmonics in texture analysis
Authors:Helmut Schaeben  K Gerald van den Boogaart
Institution:

Geoscience Mathematics and Informatics, Freiberg University of Mining and Technology, Gustav-Zeuner-Str. 12, Freiberg D-09596, Germany

Abstract:The objective of this contribution is to emphasize the fundamental role of spherical harmonics in constructive approximation on the sphere in general and in texture analysis in particular. The specific purpose is to present some methods of texture analysis and pole-to-orientation probability density inversion in a unifying approach, i.e. to show that the classic harmonic method, the pole density component fit method initially introduced as a distinct alternative, and the spherical wavelet method for high-resolution texture analysis share a common mathematical basis provided by spherical harmonics. Since pole probability density functions and orientation probability density functions are probability density functions defined on the sphere Ω3subset ofImage 3 or hypersphere Ω4subset ofImage 4, respectively, they belong at least to the space of measurable and integrable functions Image 1(Ωd), d=3, 4, respectively.

Therefore, first a basic and simplified method to derive real symmetrized spherical harmonics with the mathematical property of providing a representation of rotations or orientations, respectively, is presented. Then, standard orientation or pole probability density functions, respectively, are introduced by summation processes of harmonic series expansions of Image 1(Ωd) functions, thus avoiding resorting to intuition and heuristics. Eventually, it is shown how a rearrangement of the harmonics leads quite canonically to spherical wavelets, which provide a method for high-resolution texture analysis. This unified point of view clarifies how these methods, e.g. standard functions, apply to texture analysis of EBSD orientation measurements.

Keywords:Real-valued spherical harmonics  Real-valued harmonics for the rotation group  Harmonic series expansions  Spectral decomposition of the X-ray transform  Summability  Spherical singular integral  Spherical radial basis functions  Spherical wavelets  Methods of texture analysis
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