过程基本分四步或者三步走。第一步，加载图片。第二步，灰度化图片。第三步，Canny边缘化，第四步，检测直线或者圆。
首先，说明下OpenCv表示图片的结构是IplImage。这个东西代表了很多有用的东西。接下来的几步，都有该结构的指针对应图片。
第一步， 加载图 片。可以直接加载成灰度图，或者加载成彩色图，或者加载为原有图片的格式，第二步再灰度化。
直接加载为灰度图，IplImage* imgZero = cvLoadImage(szZero, CV_LOAD_IMAGE_GRAYSCALE);加载为彩色图，则把cvLoadImage函数的第二个参数改为CV_LOAD_IMAGE_COLOR，改为CV_LOAD_IMAGE_ANYCOLOR则保持图片原有格式。
第二步，如果第一步不是按灰度图加载，那么在这一步需要 灰度化 。代码如下，IplImage *imgGray = NULL;imgGray = cvCreateImage(cvGetSize(imgZero ),IPL_DEPTH_8U,1);cvCvtColor(imgZero, imgGray ,CV_BGR2GRAY);这几句代码的意思是根据原图片大小创建单通道位深为8的图片，然后把原有图片转换为创建的单通道8位深灰度图片。
第三步， canny处理 。代码如下，IplImage *imgCanny = cvCreateImage(cvGetSize(imgZero ),IPL_DEPTH_8U,1);cvCanny(imgGray , imgCanny, 50, 100);这几句代码的意思是根据原图片大小创建单通道位深为8的图片，然后对灰度图片进行canny处理，处理结果存储在新建立的imgCanny图片中。
第四步，使用识别函数进行 识别 直线或者圆。识别直线的函数是cvHoughLines2。识别圆的函数是cvHoughCircles。进行识别之前，先创建存储区。CvMemStorage *storage = cvCreateMemStorage(0);
识别直线的代码如下，
cvClearMemStorage(storage);
CvPoint* line;
CvSeq* lines;
lines = cvHoughLines2(imgCanny, storage, CV_HOUGH_PROBABILISTIC, 1, CV_PI/180, 50, 50, 10 );
line = (CvPoint*)cvGetSeqElem(lines, 0);
cvLine(imgZero, line[0], line[1], CV_RGB(255,0,0), 3, CV_AA, 0 );
cout<<"端点1:"<< line[0].x << "," << line[0].y<<endl;
cout<<"端点2:"<< line[1].y << "," << line[1].y<<endl;
pts[1].fX = line[0].x;
pts[1].fY = line[0].y;
识别圆的代码如下，
cvClearMemStorage(storage);
CvSeq * cir=NULL;
cir = cvHoughCircles(imgCanny, storage, CV_HOUGH_GRADIENT, 1, imgRecog->width/10 ,80,40, 50);
float * p=(float *)cvGetSeqElem(cir, 0);
CvPoint pt = cvPoint(cvRound(p[0]),cvRound(p[1]));
cvCircle(imgRecog,pt,cvRound(p[2]),CV_RGB(0,255,0));
cvCircle(imgRecog, pt, 5, CV_RGB(0,255,0), -1, 8, 0 );//绘制圆心
cout<<"圆心："<<pt.x<<","<<pt.y<<endl;
cout<<"半径："<<p[2]<<endl;
pts[0].fX = pt.x;
pts[0].fY = pt.y;
fR = p[2];
下面再提供一个识别圆和直线的程序的完整代码。识别直线和圆的参数设置，需要自己调节。
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <math.h>
#include <iostream>
#include <fstream>
using namespace std;
#pragma comment(lib, "opencv_core220.lib")
#pragma comment(lib, "opencv_highgui220.lib")
#pragma comment(lib, "opencv_imgproc220.lib")
struct Point
{
double fX;
double fY;
};
Point pts[4];
double fR;
int main()
{
//打开输出文件
ofstream outf("out.txt");
//获取cout默认输出
streambuf *default_buf=cout.rdbuf();
//重定向cout输出到文件
cout.rdbuf( outf.rdbuf() );
char* szZero = "仪表盘0.bmp";
char* szOne = "仪表盘1.bmp";
char* szRecog = "仪表盘.bmp";
IplImage* imgZero = cvLoadImage(szZero, 1);
if (!imgZero) return -1;
IplImage* imgOne = cvLoadImage(szOne, 1);
if (!imgOne) return -1;
IplImage* imgRecog = cvLoadImage(szRecog, 1);
if (!imgRecog) return -1;
IplImage *imgEdge = NULL;
imgEdge = cvCreateImage(cvGetSize(imgRecog),IPL_DEPTH_8U,1);
IplImage *imgCanny = cvCreateImage(cvGetSize(imgRecog),IPL_DEPTH_8U,1);
CvMemStorage *storage = cvCreateMemStorage(0);//内存采用默认大小
cvCvtColor(imgZero, imgEdge,CV_BGR2GRAY);
cvCanny(imgEdge, imgCanny, 50, 100);
//hough变化检测刻度0直线
cvClearMemStorage(storage);
CvPoint* line;
CvSeq* lines;
lines = cvHoughLines2(imgCanny, storage, CV_HOUGH_PROBABILISTIC, 1, CV_PI/180, 50, 50, 10 );
line = (CvPoint*)cvGetSeqElem(lines, 0);
cvLine(imgZero, line[0], line[1], CV_RGB(255,0,0), 3, CV_AA, 0 );
cout<<"端点1:"<< line[0].x << "," << line[0].y<<endl;
cout<<"端点2:"<< line[1].y << "," << line[1].y<<endl;
pts[1].fX = line[0].x;
pts[1].fY = line[0].y;
cvCvtColor(imgOne, imgEdge,CV_BGR2GRAY);
cvCanny(imgEdge, imgCanny, 50, 100);
//hough变化检测刻度1直线
cvClearMemStorage(storage);
lines = cvHoughLines2(imgCanny, storage, CV_HOUGH_PROBABILISTIC, 1, CV_PI/180, 50, 50, 10 );
line = (CvPoint*)cvGetSeqElem(lines, 0);
cvLine(imgOne, line[0], line[1], CV_RGB(255,0,0), 3, CV_AA, 0 );
cout<<"端点1:"<< line[0].x << "," << line[0].y<<endl;
cout<<"端点2:"<< line[1].y << "," << line[1].y<<endl;
pts[2].fX = line[0].x;
pts[2].fY = line[0].y;
cvCvtColor(imgRecog, imgEdge,CV_BGR2GRAY);
cvCanny(imgEdge, imgCanny, 50, 100);
//hough变化圆检测
cvClearMemStorage(storage);
CvSeq * cir=NULL;
cir = cvHoughCircles(imgCanny, storage, CV_HOUGH_GRADIENT, 1, imgRecog->width/10 ,80,40, 50);
float * p=(float *)cvGetSeqElem(cir, 0);
CvPoint pt = cvPoint(cvRound(p[0]),cvRound(p[1]));
cvCircle(imgRecog,pt,cvRound(p[2]),CV_RGB(0,255,0));
cvCircle(imgRecog, pt, 5, CV_RGB(0,255,0), -1, 8, 0 );//绘制圆心
cout<<"圆心："<<pt.x<<","<<pt.y<<endl;
cout<<"半径："<<p[2]<<endl;
pts[0].fX = pt.x;
pts[0].fY = pt.y;
fR = p[2];
//hough变化检测指针直线
lines = cvHoughLines2(imgCanny, storage, CV_HOUGH_PROBABILISTIC, 1, CV_PI/180, 50, 50, 10 );
line = (CvPoint*)cvGetSeqElem(lines, 0);
cvLine(imgRecog, line[0], line[1], CV_RGB(255,0,0), 3, CV_AA, 0 );
cout<<"端点1:"<< line[0].x << "," << line[0].y<<endl;
cout<<"端点2:"<< line[1].y << "," << line[1].y<<endl;
pts[3].fX = line[0].x;
pts[3].fY = line[0].y;
static const double PI = atan(1.0) * 4;
double fKZero = (pts[1].fY - pts[0].fY) / (pts[1].fX - pts[0].fX);
double fThetaZero = 180.0 / PI * atan(fKZero);
if (pts[1].fX + 10 < pts[0].fX)//左半部分
{
fThetaZero += 180.0;
}
fThetaZero += 360.0;
if (fThetaZero > 360.0)
{
fThetaZero -= 360.0;
}
double fKOne = (pts[2].fY - pts[0].fY) / (pts[2].fX - pts[0].fX);
double fThetaOne = 180.0 / PI * atan(fKOne);
if (pts[2].fX + 10 < pts[0].fX)//左半部分
{
fThetaOne += 180.0;
}
fThetaOne += 360.0;
if (fThetaOne > 360.0)
{
fThetaOne -= 360.0;
}
double fKRecog = (pts[3].fY - pts[0].fY) / (pts[3].fX - pts[0].fX);
double fThetaRecog = 180.0 / PI * atan(fKRecog);
if (pts[3].fX + 10 < pts[0].fX)//左半部分
{
fThetaRecog += 180.0;
}
fThetaRecog += 360.0;
if (fThetaRecog > 360.0)
{
fThetaRecog -= 360.0;
}
char szAns[100];
sprintf(szAns, "0刻度的角度为:%f,1刻度的角度为:%f,识别刻度的角度为:%f,识别结果为:%.2f",
fThetaZero, fThetaOne, fThetaRecog, (fThetaRecog - fThetaZero) / (fThetaOne - fThetaZero));
cout << szAns << endl;
cvNamedWindow("检测", CV_WINDOW_AUTOSIZE);
cvShowImage("检测", imgRecog);
cvNamedWindow("刻度0", CV_WINDOW_AUTOSIZE);
cvShowImage("刻度0", imgZero);
cvNamedWindow("刻度1", CV_WINDOW_AUTOSIZE);
cvShowImage("刻度1", imgOne);
cvWaitKey(0);
cvDestroyWindow("检测");
cvDestroyWindow("刻度0");
cvDestroyWindow("刻度1");
cvReleaseImage(&imgRecog);
cvReleaseImage(&imgZero);
cvReleaseImage(&imgOne);
cvReleaseImage(&imgEdge);
cvReleaseImage(&imgCanny);
cvReleaseMemStorage(&storage);
}