Cv2ConvexityDefects Method (InputArray, InputArray, OutputArray) OpenCvSharp Class Library
Computes the contour convexity defects

Namespace:  OpenCvSharp.CPlusPlus
Assembly:  OpenCvSharp.CPlusPlus (in OpenCvSharp.CPlusPlus.dll) Version: 1.0.0.0 (1.0.0.0)
Syntax

public static void ConvexityDefects(
	InputArray contour,
	InputArray convexHull,
	OutputArray convexityDefects
)

Parameters

contour
Type: OpenCvSharp.CPlusPlusInputArray
Input contour.
convexHull
Type: OpenCvSharp.CPlusPlusInputArray
Convex hull obtained using convexHull() that should contain indices of the contour points that make the hull.
convexityDefects
Type: OpenCvSharp.CPlusPlusOutputArray
The output vector of convexity defects. Each convexity defect is represented as 4-element integer vector (a.k.a. cv::Vec4i): (start_index, end_index, farthest_pt_index, fixpt_depth), where indices are 0-based indices in the original contour of the convexity defect beginning, end and the farthest point, and fixpt_depth is fixed-point approximation (with 8 fractional bits) of the distance between the farthest contour point and the hull. That is, to get the floating-point value of the depth will be fixpt_depth/256.0.
See Also

Reference