“…Besides the use of edge orientation as that in GHT, these major modifications include: the simultaneous consideration of a range of circle radii [12], [14], [15], use of a complex accumulator array with radius modulated phase [15]- [17], incorporation of different sampling strategies [18]- [21], exploration of the symmetry [3], [22], [23], adoption of the hierarchical structure [24], and the implementation of the circle detection as filtering operations [17]. It is worth noting that these modifications are not isolated, in fact, they usually work in cooperation.…”