compactness — Shape factor for the compactness of a region.
The operator compactness calculates the compactness of the input regions.
If L is the length of the contour (see contlength) and F the area of the region the shape factor C is defined as:
C' = L^2 / (4 F pi)
C = max(1,C')
The shape factor C of a circle is 1. If the region is long or has holes C is larger than 1. The operator compactness responds to the course of the contour (roughness) and to holes. 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 case of an empty region the operator compactness 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.
Compactness of the input region(s).
Assertion: Compactness >= 1.0 || Compactness == 0
The operator compactness 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
contlength, area_center, select_shape