CV_EXPORTS_W void approxPolyDP( InputArray curve,
OutputArray approxCurve,
double epsilon, bool closed );
@param curve Input vector of a 2D point stored in std::vector or Mat
@param approxCurve Result of the approximation. The type should match the type of the input curve.
@param epsilon Parameter specifying the approximation accuracy. This is the maximum distance
between the original curve and its approximation.
@param closed If true, the approximated curve is closed (its first and last vertices are
connected). Otherwise, it is not closed.
The function cv::approxPolyDP approximates a curve or a polygon with another curve/polygon with less
vertices so that the distance between them is less or equal to the specified precision. It uses the
Douglas-Peucker algorithm <http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm>
主要功能是把一个连续光滑曲线折线化：
参数有4个：
InputArray curve：输入曲线，数据类型可以为vector<Point>。
OutputArray approxCurve：输出折线，数据类型可以为vector<Point>。
double epsilon：判断点到相对应的line segment 的距离的阈值。（距离大于此阈值则舍弃，小于此阈值则保留，epsilon越小，折线的形状越“接近”曲线。）
bool closed：曲线是否闭合的标志位。
程序示例：
#include<opencv2/opencv.hpp>
#include<iostream>
using namespace std;
using namespace cv;
void main()
{
Mat srcImg = imread("01.jpg");
imshow("src", srcImg);
Mat dstImg(srcImg.size(), CV_8UC3, Scalar::all(0));//纯黑图像
cvtColor(srcImg, srcImg, CV_BGR2GRAY);
threshold(srcImg, srcImg, 200, 255, CV_THRESH_BINARY_INV);
vector<vector<Point>> contours;
vector<Vec4i> hierarcy;
findContours(srcImg, contours, hierarcy, 0, CV_CHAIN_APPROX_NONE);
vector<vector<Point>> contours_poly(contours.size());//用于存放折线点集
for (int i = 0; i<contours.size(); i++)
{
approxPolyDP(Mat(contours[i]), contours_poly[i], 15, true);
drawContours(dstImg, contours_poly, i, Scalar(0, 255, 255), 2, 8); //绘制
}
imshow("approx", dstImg);
waitKey(0);
}
图像“01.jpg”：
epsilon为15：
epsilon为5：
