More specifically, the first part is a 1D vector which carries
the radiuses of the best fitted circle of the curves that belong to
the outer shell of the vessel’s main body at each contouring
level. A graph depiction of this vector is visually similar to a
quantized version of the vessel’s body outer profile. The
second part of the descriptor encodes the properties of all
curves that belong to the appendages group in a 2D binary
array. This time, the position of the best fitted circle of each
curve is quantized into a predefined area-sector around the unit
circle (Fig. 1). The columns of the binary array indicate the
sectors while the rows indicate the contouring level in which
each curve belongs [5]. In our tests we have selected π/8 as the
angle step between two consecutive unit circle sectors.