如何使用OpenCV cvProjectPoints2函数

Question

我在使用cvProjectPoints2函数时遇到了一些麻烦.以下是O'Reilly的"Learning OpenCV"一书的功能概述:

void cvProjectPoints2(
const CvMat* object_points,
const CvMat* rotation_vector,
const CvMat* translation_vector,
const CvMat* intrinsic_matrix,
const CvMat* distortion_coeffs,
CvMat* image_points,
);

第一个参数object_points是你想要投射的点数列表; 它只是一个包含点位置的N×3矩阵.您可以在对象自己的局部坐标系中给出这些,然后提供3×1矩阵rotation_vector*并将translation_vector两个坐标相关联.如果在您的特定环境中直接在摄像机坐标中工作更容易,那么您可以object_points在该系统中放入并设置两者rotation_vector并translation_vector包含0.†

的intrinsic_matrix和distortion_coeffs仅仅是相机固有信息和来自cvCalibrateCamera2()中第11章所讨论的失真系数image_points的参数是N×2矩阵到其中的运算结果将被写入.

首先,object_points数组似乎存在错误.如果只有一个点,即N = 1,则程序崩溃.无论如何,我有几个相机内部参数和投影矩阵.失真系数为0,即没有失真.为简单起见,假设我有2个摄像头:

double intrinsic[2][3][3] = {
//camera 0
1884.190000,    0, 513.700000,
0.0,    1887.490000,    395.609000,
0.0,    0.0,    1.0,
//camera 4
1877.360000,    0.415492,   579.467000,
0.0,    1882.430000,    409.612000,
0.0,    0.0,    1.0
};

double projection[2][3][4] = {
//camera 0
0.962107,   -0.005824,  0.272486,   -14.832727,
0.004023,   0.999964,   0.007166,   0.093097,
-0.272519,  -0.005795,  0.962095,   -0.005195,
//camera 4
1.000000,   0.000000,   -0.000000,  0.000006,
0.000000,   1.000000,   -0.000000,  0.000001,
-0.000000,  -0.000000,  1.000000,   -0.000003
};

据我了解,此信息足以投影任何相机视图上的任何点(x,y,z).这里,在x,y,z坐标中,摄像机4的光学中心是世界坐标的原点.

这是我的代码:

#include <cv.h>
#include <highgui.h>
#include <cvaux.h>
#include <cxcore.h>
#include <stdio.h>

double intrinsic[2][3][3] = {
//0
1884.190000,    0, 513.700000,
0.0,    1887.490000,    395.609000,
0.0,    0.0,    1.0,
//4
1877.360000,    0.415492,   579.467000,
0.0,    1882.430000,    409.612000,
0.0,    0.0,    1.0
};

double projection[2][3][4] = {
//0
0.962107,   -0.005824,  0.272486,   -14.832727,
0.004023,   0.999964,   0.007166,   0.093097,
-0.272519,  -0.005795,  0.962095,   -0.005195,
//4
1.000000,   0.000000,   -0.000000,  0.000006,
0.000000,   1.000000,   -0.000000,  0.000001,
-0.000000,  -0.000000,  1.000000,   -0.000003
};


int main() {
    CvMat* camera_matrix[2]; //
    CvMat* rotation_matrix[2]; //
    CvMat* dist_coeffs[2]; 
    CvMat* translation[2];
    IplImage* image[2];
    image[0] = cvLoadImage("color-cam0-f000.bmp", 1);
    image[1] = cvLoadImage("color-cam4-f000.bmp", 1);
    CvSize image_size;
    image_size = cvSize(image[0]->width, image[0]->height);

    for (int m=0; m<2; m++) {
        camera_matrix[m] = cvCreateMat(3, 3, CV_32F);
        dist_coeffs[m] = cvCreateMat(1, 4, CV_32F);
        rotation_matrix[m] = cvCreateMat(3, 3, CV_32F);
        translation[m] = cvCreateMat(3, 1, CV_32F);
    }

    for (int m=0; m<2; m++) {
        for (int i=0; i<3; i++)
            for (int j=0; j<3; j++) {
                cvmSet(camera_matrix[m],i,j, intrinsic[m][i][j]);
                cvmSet(rotation_matrix[m],i,j, projection[m][i][j]);
            }
        for (int i=0; i<4; i++)
            cvmSet(dist_coeffs[m], 0, i, 0);
        for (int i=0; i<3; i++)
            cvmSet(translation[m], i, 0, projection[m][i][3]);
    }

    CvMat* vector = cvCreateMat(3, 1, CV_32F);
    CvMat* object_points = cvCreateMat(10, 3, CV_32F);
    cvmSet(object_points, 0, 0, 1000);
    cvmSet(object_points, 0, 1, 500);
    cvmSet(object_points, 0, 2, 100);

    CvMat* image_points = cvCreateMat(10, 2, CV_32F);
    int m = 0;
    cvRodrigues2(rotation_matrix[m], vector);
    cvProjectPoints2(object_points, vector, translation[m], camera_matrix[m], dist_coeffs[m], image_points);
    printf("%f\n", cvmGet(image_points, 0, 0));
    printf("%f\n", cvmGet(image_points, 0, 1));
    return 0;
}

图像是1024*768,并且z的可见部分知道在44和120之间.因此,应该在两个相机上看到该点,对吧？但结果绝对错误.即使m = 1.我做错了什么？

Answer 1

是的，cvProjectPoints 用于投影点数组。您可以使用简单的矩阵运算来投影一个点：

CvMat *pt = cvCreateMat(3, 1, CV_32FC1);
CvMat *pt_rt = cvCreateMat(3, 1, CV_32FC1);
CvMat *proj_pt = cvCreateMat(3, 1, CV_32FC1);
cvMatMulAdd(rotMat, pt, translation, pt_rt);
cvMatMul(intrinsic, pt_rt, proj_pt);
// convertPointsHomogenious might be used
float scale = (float)CV_MAT_ELEM(*proj_pt, float, 2, 0); 
float x = CV_MAT_ELEM(*proj_pt, float, 0, 0) / scale;
float y = CV_MAT_ELEM(*proj_pt, float, 1, 0) / scale;
CvPoint2D32f img_pt = cvPoint2D32f(x, y);