The quantification of anisotropy —its main direction and the degree of dispersion around it— is desirable in numerous research fields dealing with physical structures. Conventional methods are based on the orientation of interface elements. The results of these methods do not always agree with perceived anisotropy, and anisotropic structures do not necessarily turn out to be 'anisotropic' using these methods. In the present paper, we propose an alternative to curve and surface orientation, namely volume orientation. Using trabecular bone as an example of a two-phase anisotropic structure, the new concept is studied in some detail. In particular, a parametric method of estimating volume orientation from sections is presented and discussed.
Keywords: Anisotropy; Dimroth-Watson distribution; directional statistics; exponential families; point-sampling; stereology; surface orientation; trabecular bone; volume orientation