diff --git a/modules/imgproc/doc/pics/minenclosingtriangle.png b/modules/imgproc/doc/pics/minenclosingtriangle.png new file mode 100644 index 000000000..ec89c6aa2 Binary files /dev/null and b/modules/imgproc/doc/pics/minenclosingtriangle.png differ diff --git a/modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst b/modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst index d34600669..c091ba3b0 100644 --- a/modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst +++ b/modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst @@ -560,6 +560,41 @@ The function finds the four vertices of a rotated rectangle. This function is us +minEnclosingTriangle +---------------------- +Finds a triangle of minimum area enclosing a 2D point set. + +.. ocv:function:: void minEnclosingTriangle( InputArray points, OutputArray triangle ) + +.. ocv:function:: void minEnclosingTriangle( InputArray points, OutputArray triangle, double &area ) + +.. ocv:pyfunction:: cv2.minEnclosingTriangle(points[, triangle]) -> triangle, area + + :param points: Input vector of 2D points with depth ``CV_32S`` or ``CV_32F``. + + :param triangle: Output vector of three 2D points defining the vertices of the triangle. The depth of the OutputArray must be ``CV_32F``. + + :param area: The area of the minimum enclosing triangle. + +The output for a given 2D point set is shown in the image below. The 2D points are depicted in *red* and the enclosing triangle in *yellow*. + +.. image:: pics/minenclosingtriangle.png + :height: 250px + :width: 250px + :alt: Sample output of the minimum enclosing triangle function + +The implementation of the algorithm is based on O'Rourke's [ORourke86]_ and Klee and Laskowski's [KleeLaskowski85]_ papers. O'Rourke provides a +:math:`\theta(n)` +algorithm for finding the minimal enclosing triangle of a 2D convex polygon with ``n`` vertices. Since the :ocv:func:`minEnclosingTriangle` function takes a 2D point set as input an additional preprocessing step of computing the convex hull of the 2D point set is required. The complexity of the :ocv:func:`convexHull` function is +:math:`O(n log(n))` which is higher than +:math:`\theta(n)`. +Thus the overall complexity of the function is +:math:`O(n log(n))`. + +.. note:: See ``opencv_source/samples/cpp/minarea.cpp`` for a usage example. + + + minEnclosingCircle ---------------------- Finds a circle of the minimum area enclosing a 2D point set. @@ -672,6 +707,10 @@ See below a sample output of the function where each image pixel is tested again .. [Hu62] M. Hu. *Visual Pattern Recognition by Moment Invariants*, IRE Transactions on Information Theory, 8:2, pp. 179-187, 1962. +.. [KleeLaskowski85] Klee, V. and Laskowski, M.C., *Finding the smallest triangles containing a given convex polygon*, Journal of Algorithms, vol. 6, no. 3, pp. 359–375 (1985) + +.. [ORourke86] O’Rourke, J., Aggarwal, A., Maddila, S., and Baldwin, M., *An optimal algorithm for finding minimal enclosing triangles*, Journal of Algorithms, vol. 7, no. 2, pp. 258–269 (1986) + .. [Sklansky82] Sklansky, J., *Finding the Convex Hull of a Simple Polygon*. PRL 1 $number, pp 79-83 (1982) .. [Suzuki85] Suzuki, S. and Abe, K., *Topological Structural Analysis of Digitized Binary Images by Border Following*. CVGIP 30 1, pp 32-46 (1985)