The 3D ellipsoid fitting plugin will fit a 3D ellipsoid to objects in a labelled image.
The ellipsoid axes and radii are computed using 3D moments :
The three eigen values and vectors are then computed from this matrix :
The three radii are then : √(5*eigen value)
The different results are :
Object and fitted ellipsoid with main elongation axis
Bounding box and oriented bounding box