简单的理解就是首先对纯粹的直线（确实是一条直线，没有断点），根据参数maxLineGap进行连接，然后在对是否满足参数threshold和minLineLength进行判断，最后返回直线。
实例
#include "stdafx.h"
#include <cv.h>
#include <highgui.h>
#include <math.h>
using namespace cv;
int main(int argc, char** argv)
{
Mat src, dst, color_dst;
src=imread("F:\\pic\\linecjc1.jpg", 0);
Canny( src, dst, 50, 200, 3 );
cvtColor( dst, color_dst, CV_GRAY2BGR );
vector<Vec4i> lines;
HoughLinesP( dst, lines, 1, CV_PI/180, 10, 10, 0);
for( size_t i = 0; i < lines.size(); i++ )
{
line( color_dst, Point(lines[i][0], lines[i][1]),
Point(lines[i][2], lines[i][3]), Scalar(0,0,255), 1, 8 );
}
namedWindow( "Source", 1 );
imshow( "Source", src );
namedWindow( "Detected Lines", 1 );
imshow( "Detected Lines", color_dst );
waitKey(0);
return 0;
}