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This is a family of synthetic diffusion tensor volumes. The tensor's eigenvectors are always aligned along lines of longitude and latitude. In this case (upper left), there's total linear anisotropy, aligned along these circles, and in this case (lower right), the linear anisotropy is aligned along lines going from pole to pole. Half-way between (center), there's planar anisotropy, and in that case, it looks like normal surface shading.

The point to remember is that even though these look like surface shading of spheres with some anisotropic reflection model, these are actually direct volume renderings of these datasets, using the lit-tensor shading model. Now lets put all these different pieces together.