将单纯形矩阵分解为旋转矩阵和平移向量

Question

I'm working on an augmented reality application for android using opencv 2.4.4 and have some problem with homography decomposition. As we know, homography matrix is define as H=A.[R t] , where A is the intrinsic camera matrix, R is rotation matrix and t is translation vector. I want to estimate the view side of camera using pictures, also the orientation of camera in 3d room.

Homography matrix can I estimate with opencv function: findHomography, and I think it works!!! Here how I do it:

static Mat mFindHomography(MatOfKeyPoint keypoints1, MatOfKeyPoint keypoints2, MatOfDMatch matches){
    List<Point> lp1 = new ArrayList<Point>(500);
    List<Point> lp2 = new ArrayList<Point>(500);

    KeyPoint[] k1 = keypoints1.toArray();
    KeyPoint[] k2 = keypoints2.toArray();

    List<DMatch> matchesList = matches.toList();

    if (matchesList.size() < 4){
        MatOfDMatch mat = new MatOfDMatch();
        return mat;
    }

    // Add matches keypoints to new list to apply homography
    for(DMatch match : matchesList){
        Point kk1 = k1[match.queryIdx].pt;
        Point kk2 = k2[match.trainIdx].pt;
        lp1.add(kk1);
        lp2.add(kk2);
    }

    MatOfPoint2f srcPoints = new MatOfPoint2f(lp1.toArray(new Point[0]));
    MatOfPoint2f dstPoints  = new MatOfPoint2f(lp2.toArray(new Point[0]));

    Mat mask = new Mat();

    Mat homography = Calib3d.findHomography(srcPoints, dstPoints, Calib3d.RANSAC, 10, mask); // Finds a perspective transformation between two planes. ---Calib3d.LMEDS Least-Median robust method 

    List<DMatch> matches_homo = new ArrayList<DMatch>();
    int size = (int) mask.size().height;
    for(int i = 0; i < size; i++){          
        if ( mask.get(i, 0)[0] == 1){
            DMatch d = matchesList.get(i);
            matches_homo.add(d);
        }
    }

    MatOfDMatch mat = new MatOfDMatch();
    mat.fromList(matches_homo);

    matchesFilterdByRansac = (int) mat.size().height;
    return homography;
}

After that, I want to decompose this homography matrix and compute euler angles. As we know H=A.[R t], I multiply homography matrix with inverse of camera intrinsic matrix: HA^{-1} = [R t]. So, I want to decompose [R t] in rotation and translation and compute euler angles from rotation matrix. But it didn't work. What is wrong there?!!

if(!homography.empty()){ // esstimate pose frome homography 
Mat intrinsics = Mat.zeros(3, 3, CvType.CV_32FC1);  // camera intrinsic matrix 
intrinsics.put(0, 0, 890);
intrinsics.put(0, 2, 400);
intrinsics.put(1, 1, 890);
intrinsics.put(1, 2, 240);
intrinsics.put(2, 2, 1);

// Inverse Matrix from Wolframalpha
double[] inverseIntrinsics = { 0.001020408, 0 , -0.408163265,
        0, 0.0011235955, -0.26966292,
        0, 0 , 1 }; 

// cross multiplication 
double[] rotationTranslation = matrixMultiply3X3(homography, inverseIntrinsics);

Mat pose = Mat.eye(3, 4, CvType.CV_32FC1);  // 3x4 matrix, the camera pose
float norm1 = (float) Core.norm(rotationTranslation.col(0));
float norm2 = (float) Core.norm(rotationTranslation.col(1));
float tnorm = (norm1 + norm2) / 2.0f;       // Normalization value  ---test: float tnorm = (float) h.get(2, 2)[0];// not worked

Mat normalizedTemp = new Mat();
Core.normalize(rotationTranslation.col(0), normalizedTemp);
normalizedTemp.convertTo(normalizedTemp, CvType.CV_32FC1);
normalizedTemp.copyTo(pose.col(0)); // Normalize the rotation, and copies the column to pose

Core.normalize(rotationTranslation.col(1), normalizedTemp);
normalizedTemp.convertTo(normalizedTemp, CvType.CV_32FC1);    
normalizedTemp.copyTo(pose.col(1));// Normalize the rotation and copies the column to pose

Mat p3 = pose.col(0).cross(pose.col(1)); // Computes the cross-product of p1 and p2
p3.copyTo(pose.col(2));// Third column is the crossproduct of columns one and two

double[] buffer = new double[3];
rotationTranslation.col(2).get(0, 0, buffer);
pose.put(0, 3, buffer[0] / tnorm);  //vector t [R|t] is the last column of pose
pose.put(1, 3, buffer[1] / tnorm);
pose.put(2, 3, buffer[2] / tnorm);

float[] rotationMatrix = new float[9];
rotationMatrix = getArrayFromMat(pose);

float[] eulerOrientation = new float[3];
SensorManager.getOrientation(rotationMatrix, eulerOrientation); 

// Convert radian to degree
double yaw = (double) (eulerOrientation[0]) * (180 / Math.PI));// * -57;
double pitch = (double) (eulerOrientation[1]) * (180 / Math.PI));
double roll = (double) (eulerOrientation[2]) * (180 / Math.PI));}

Note that opencv 3.0 has a homogeraphy decomposition function ( here ), but I'm using opencv 2.4.4 for android!!! Is there a wrapper for it in java?

Second problem is with decomposing of rotation matrix in euler angels. Is there any problem with:

    float[] eulerOrientation = new float[3];
SensorManager.getOrientation(rotationMatrix, eulerOrientation); 

I used this link too, but not better result!

double pitch = Math.atan2(pose.get(2, 1)[0], pose.get(2, 2)[0]);
double roll = Math.atan2(-1*pose.get(2, 0)[0], Math.sqrt( Math.pow(pose.get(2, 1)[0], 2) + Math.pow(pose.get(2, 2)[0], 2)) );
double yaw = Math.atan2(pose.get(1, 0)[0], pose.get(0, 0)[0]);

Thanks a lot for any response

Answer 1

I hope this answer will help those looking for a solution today.

My answer uses c++ and opencv 2.4.9. I copied the decomposehomographymat function from opencv 3.0. After computing homography I use the copied function to decompose homography. To filter homography matrix and select the correct answer from the 4 decompositions, check my answer here .

To obtain euler angles from the rotation matrix, you can refer to this . I am able to get good results with this method.