When the angle θ sweeps through the full 360 degree range the points (x,y) trace the perimeter of a circle.If an image contains many points, some of which fall on perimeters of circles, then the job of the search program is to find parameter triplets (a,b,R) to describe each circle. The fact that the parameter space is 3D makes a direct implementation of the Hough technique more expensive in computer memory and time.