文章目录
- 一、简介
- 二、效果演示
一、简介
比较常见的判断点与多边形关系的算法有射线法、面积法、点线判断法和弧长法等,算法复杂度都为O(n),不过只有射线法可以正确用于凹多边形,其他3个只可以用于凸多边形。
测试一个点是否在给定的多边形内部,边缘或者外部
InputArray contour, 输入的轮廓
Point2f
pt, 测试点
bool
measureDist 是否返回距离值,若为false(1在内面,0在边界上,-1在外部),true返回实际距离(double类型)
)
代码演示:
- 构建一张400x400大小的图片, Mat::Zero(400, 400, CV_8UC1)
- 画上一个多边形的闭合区域line
- 查找轮廓
- 对图像中所有像素点做点 多边形测试,得到距离,归一化后显示。
头文件 quick_opencv.h
:声明类与公共函数
#pragma once
#include <opencv2\opencv.hpp>
using namespace cv;
class QuickDemo {
public:
...
void points_polygons_Demo();
};
主函数调用该类的公共成员函数
#include <opencv2\opencv.hpp>
#include <quick_opencv.h>
#include <iostream>
using namespace cv;
int main(int argc, char** argv) {
Mat src = imread("D:\\Desktop\\maomao.png");
if (src.empty()) {
printf("Could not load images...\n");
return -1;
}
namedWindow("input", WINDOW_NORMAL);
imshow("input", src);
QuickDemo qk;
qk.points_polygons_Demo();
waitKey(0);
destroyAllWindows();
return 0;
}
二、效果演示
源文件 quick_demo.cpp
:实现类与公共函数
void QuickDemo::points_polygons_Demo() {
// 定义六边形
const int r = 100;
Mat src = Mat::zeros(r * 4, r * 4, CV_8UC1);
vector<Point2f> vert(6);
vert[0] = Point(3 * r / 2, static_cast<int>(1.34 * r));
vert[1] = Point(1 * r, 2 * r);
vert[2] = Point(3 * r / 2, static_cast<int>(2.68 * r));
vert[3] = Point(5 * r / 2, static_cast<int>(2.68 * r));
vert[4] = Point(3 * r, 2 * r);
vert[5] = Point(5 * r / 2, static_cast<int>(1.34 * r));
// 绘制六边形
for (int i = 0; i < 6; i++) {
line(src, vert[i], vert[(i + 1) % 6], Scalar(255), 3, 8);
}
imshow("src", src);
// 查找轮廓
vector<vector<Point>> contours;
vector<Vec4i> hieracrhy;
Mat src_copy = src.clone();
findContours(src_copy, contours, hieracrhy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
// 计算图像所有点到轮廓的距离
float* dst_ptr;
Mat raw_dist = Mat::zeros(src_copy.size(), CV_32FC1);
for (int row = 0; row < src_copy.rows; row++) {
dst_ptr = raw_dist.ptr<float>(row);
for (int col = 0; col < src_copy.cols; col++) {
*dst_ptr++ = saturate_cast<float>(pointPolygonTest(contours[0], Point2f((float)col, (float)row), true));
}
}
// 获取点到轮廓的距离的最大最小值
double minValue, maxValue;
minMaxLoc(raw_dist, &minValue, &maxValue, 0, 0, Mat());
minValue = abs(minValue);
maxValue = abs(maxValue);
// 绘制距离映射图
float* dist_ptr;
Mat drawImg = Mat::zeros(src.size(), CV_8UC3);
for (int row = 0; row < drawImg.rows; row++) {
dist_ptr = raw_dist.ptr<float>(row);
for (int col = 0; col < drawImg.cols; col++) {
float distance_ = *dist_ptr++;
if (distance_ > 0) {
drawImg.at<Vec3b>(row,col)[0] = (uchar)((abs(1.0 - distance_ / maxValue)) * 255);
}
else if (distance_ < 0) {
drawImg.at<Vec3b>(row, col)[2] = (uchar)((abs(1.0 - distance_ / minValue)) * 255);
}
else {
drawImg.at<Vec3b>(row, col)[0] = (uchar)(255);
drawImg.at<Vec3b>(row, col)[1] = (uchar)(255);
drawImg.at<Vec3b>(row, col)[2] = (uchar)(255);
}
}
}
imshow("drawImg", drawImg);
}