shapeaxis - compute the axis/orientation of 3d shapes

Provides a vector describing the major axis of any 3d shape represented by a grayscale 3d array.

Shapeaxis determines the major axis of 3d shapes that are encoded within volumetric grayscale arrays. Only useful for shapes that have a real major axis/midline orientation. Allows easy plotting of the shape axis. Intended to make it easy to use imrotate3 for shape-centric rotational operations, a the produced vector is in that axis format.

Outputs the object center if desired, and accept an optional second argument to threshold the grayscale intensity required for a pixel to contribute to the calculations.