circularity — Shape factor for the circularity (similarity to a circle) of a region.
The operator circularity calculates the similarity of the input region with a circle.
If F is the area of the region and max is the maximum distance from the center to all contour pixels, the shape factor C is defined as:
C = min(1,C')
The shape factor C of a circle is 1. If the region is long or has holes, C is smaller than 1. The operator circularity especially responds to large bulges, holes and unconnected regions. The value of C is clipped to 1.0, because the pixel area of a region can only be an approximation of a real circle's area. This approximation error is bigger for small regions than for large regions.
In the documentation of this chapter (Regions / Features), you can find an image illustrating regions which vary in their circularity.
In case of an empty region the operator circularity returns the value 0 (if no other behavior was set (see set_system)). If more than one region is passed the numerical values of the shape factor are stored in a tuple, the position of a value in the tuple corresponding to the position of the region in the input tuple.
Region(s) to be examined.
Circularity of the input region(s).
Assertion: 0 <= Circularity && Circularity <= 1.0
* Comparison between shape factors of rectangle, circle and ellipse: gen_rectangle1(R1,10,10,20,20) gen_rectangle2(R2,100,100,0.0,100,20) gen_ellipse(E100,100,100,0.0,100,20) gen_circle(C,100,100,20) circularity(R1,M_R1) circularity(R2,M_R2) circularity(E100,M_E) circularity(C,M_C) fwrite_string(FileId,['quadrate: ',M_R1]) fnew_line(FileId) fwrite_string(FileId,['rectangle: ',M_R2]) fnew_line(FileId) fwrite_string(FileId,['ellipse: ',M_E]) fnew_line(FileId) fwrite_string(FileId,['circle: ',M_C]) fnew_line(FileId)
The operator circularity returns the value 2 (H_MSG_TRUE) if the input is not empty. The behavior in case of empty input (no input regions available) is set via the operator set_system('no_object_result',<Result>). The behavior in case of empty region (the region is the empty set) is set via set_system('empty_region_result',<Result>). If necessary an exception is raised.
threshold, regiongrowing, connection
roundness, compactness, convexity, eccentricity