circularity (Operator)

Name

circularity — Shape factor for the circularity (similarity to a circle) of a region.

Synopsis

circularity(Regions : : : Circularity)

Description

The operator circularity calculates the similarity of the input region with a circle.

Calculation: 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 = F / (max^2 * pi)

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.

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.

Parameters

Regions (input_object)	region(-array) → object
Region(s) to be examined.

Circularity (output_control)	real(-array) → (real)
Roundness of the input region(s).
Assertion: (0 <= Circularity) && (Circularity <= 1.0)

Example

* 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(E100,100,0.0,100,20)
gen_circle(C,100,100,20)
circularity([R1,R2,E,C],M)
fwrite_string(FileId,['quadrate:  ',M[1]])
fnew_line(FileId)
fwrite_string(FileId,['rectangle: ',M[2]])
fnew_line(FileId)
fwrite_string(FileId,['ellipse:   ',M[3]])
fnew_line(FileId)
fwrite_string(FileId,['circle:    ',M[4]])
fnew_line(FileId)

Result

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.

Parallelization Information

circularity is reentrant and automatically parallelized (on tuple level).

Possible Predecessors

threshold, regiongrowing, connection

Alternatives

roundness, compactness, convexity, eccentricity

See also

area_center, select_shape

Module

Foundation