The data that are used in this descriptor are extracted from
the curves that are produced after contouring the vessel’s 3D
mesh at multiple levels parallel to the X-Z plane defined by a
right handed 3D Cartesian coordinates system. Those curves
are grouped into those that belong the main body of the vessel
and those that belong to the appendages. Each curve is
described by a number of points and an index list of pointers
that organises them into line segments. Circular regression is
performed for each curve in both groups. Thus, properties such
as the centre of gravity of the best fitted circle, its radius and
the circle fitting error are computed. The descriptor is divided
into two parts. The first part is used to describe the main body
of the vessel while the second encodes the appendages
positions in the unit circle.