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I am using OpenCV 3.1 and I am trying to estimate the rotation between two frames of a camera. First, I detect some keypoints, define their descriptors and match them. Finally, I have to see the rotation with solvePnPRansac (supposing all points lay on the z=0 plane), but it does always return the identity matrix as the rotation even though the image is rotated. Here is the part of the code that does not seem to work: (Get_Euler_angles is a function I made and works)

std::vector< DMatch > good_matches; for( int i = 0; i < descriptors_object.rows; i++ ) { if( matches[i].distance <= factor*min_dist ) { good_matches.push_back( matches[i]); } }

std::vector<point3f> obj3; std::vector<point2f> scene2; Point3f aux3; Point2f aux2;

for( size_t i = 0; i < good_matches.size(); i++ ) { //-- Get the keypoints from the good matches aux3.x=keypoints_object[ good_matches[i].queryIdx ].pt.x; aux3.y=keypoints_object[ good_matches[i].queryIdx ].pt.y; aux3.z=0; obj3.push_back(aux3); aux2.x=keypoints_object[ good_matches[i].queryIdx ].pt.x; aux2.y=keypoints_object[ good_matches[i].queryIdx ].pt.y; scene2.push_back(aux2); }

Mat rvec, tvec, rmat; Mat cameraMatrix = (Mat_<float>(3,3) << 374.67,0,320.5,0,374.67,180.5,0,0,1); solvePnPRansac( obj3, scene2, cameraMatrix, noArray(), rvec, tvec); Rodrigues(rvec, rmat);

std::vector<double> euler_angles (3); std::cout << "rvec from solvePnPRansac: " << std::endl << rvec << std::endl; std::cout << "rmat from solvePnPRansac: " << std::endl << rmat << std::endl; euler_angles=get_Euler_angles(rmat); std::cout << "euler angles from solvePnPRansac: " << std::endl << "[" << euler_angles[0] << " "<< euler_angles[1] << " " << euler_angles[2] << "]" << std::endl; std::cout << "tvec from solvePnPRansac: " << std::endl << tvec << std::endl;

If I use two images as input I get the matches and a translation vector, but rotation vector is empty:

rvec from solvePnPRansac: [0; 0; 0] rmat from solvePnPRansac: [1, 0, 0; 0, 1, 0; 0, 0, 1] euler angles from solvePnPRansac: [-0 0 0] tvec from solvePnPRansac: [-320.5000258050974; -180.4999954623273; 374.6697010743459]

I am using OpenCV 3.1 and I am trying to estimate the rotation between two frames of a camera. First, I detect some keypoints, define their descriptors and match them. Finally, I have to see the rotation with solvePnPRansac (supposing all points lay on the z=0 plane), but it does always return the identity matrix as the rotation even though the image is rotated. Here is the part of the code that does not seem to work: (Get_Euler_angles is a function I made and works)

std::vector< DMatch > good_matches; good_matches;

for( int i = 0; i < descriptors_object.rows; i++ ) {

 if( matches[i].distance <= factor*min_dist )
      { good_matches.push_back( matches[i]); }
 

}

std::vector<point3f> obj3; obj3;

std::vector<point2f> scene2; scene2;

Point3f aux3; aux3;

Point2f aux2;

for( size_t i = 0; i < good_matches.size(); i++ ) { )

{

//-- Get the keypoints from the good matches
  aux3.x=keypoints_object[ good_matches[i].queryIdx ].pt.x;
  aux3.y=keypoints_object[ good_matches[i].queryIdx ].pt.y;
  aux3.z=0;
  obj3.push_back(aux3);
  aux2.x=keypoints_object[ good_matches[i].queryIdx ].pt.x;
  aux2.y=keypoints_object[ good_matches[i].queryIdx ].pt.y;
  scene2.push_back(aux2);
 

}

Mat rvec, tvec, rmat; rmat;

Mat cameraMatrix = (Mat_<float>(3,3) << 374.67,0,320.5,0,374.67,180.5,0,0,1); 374.67,0,320.5,0,374.67,180.5,0,0,1);

solvePnPRansac( obj3, scene2, cameraMatrix, noArray(), rvec, tvec); tvec);

Rodrigues(rvec, rmat);

std::vector<double> euler_angles (3); (3);

std::cout << "rvec from solvePnPRansac: " << std::endl << rvec << std::endl; std::endl;

std::cout << "rmat from solvePnPRansac: " << std::endl << rmat << std::endl; euler_angles=get_Euler_angles(rmat); std::endl;

euler_angles=get_Euler_angles(rmat);

std::cout << "euler angles from solvePnPRansac: " << std::endl << "[" << euler_angles[0] << " "<< euler_angles[1] << " " << euler_angles[2] << "]" << std::endl; std::endl;

std::cout << "tvec from solvePnPRansac: " << std::endl << tvec << std::endl;

If I use two images as input I get the matches and a translation vector, but rotation vector is empty:

rvec from solvePnPRansac: [0; 0; 0]

[0;

0;

0]

rmat from solvePnPRansac:

[1, 0, 0; 0;

0, 1, 0; 0;

0, 0, 1] 1]

euler angles from solvePnPRansac:

[-0 0 0] 0]

tvec from solvePnPRansac: [-320.5000258050974; -180.4999954623273;

[-320.5000258050974;

-180.4999954623273;

374.6697010743459]

I am using OpenCV 3.1 and I am trying to estimate the rotation between two frames of a camera. First, I detect some keypoints, define their descriptors and match them. Finally, I have to see the rotation with solvePnPRansac (supposing all points lay on the z=0 plane), but it does always return the identity matrix as the rotation even though the image is rotated. Here is the part of the code that does not seem to work: (Get_Euler_angles is a function I made and works)works:

 std::vector< DMatch > good_matches;
 
good_matches;
for( int i = 0; i < descriptors_object.rows; i++ )
{ 
 
  if( matches[i].distance <= factor*min_dist )
 { good_matches.push_back( matches[i]); }
 
 } 
 
std::vector<point3f> obj3;
 
std::vector<point2f> scene2;
 

std::vector<Point3f> obj3;
std::vector<Point2f> scene2;
Point3f aux3;
 
aux3;
Point2f aux2;
 
aux2;
for( size_t i = 0; i < good_matches.size(); i++ )
 
{
 
)
{
//-- Get the keypoints from the good matches
 aux3.x=keypoints_object[ good_matches[i].queryIdx ].pt.x;
 aux3.y=keypoints_object[ good_matches[i].queryIdx ].pt.y;
 aux3.z=0;
 obj3.push_back(aux3);
 aux2.x=keypoints_object[ good_matches[i].queryIdx ].pt.x;
 aux2.y=keypoints_object[ good_matches[i].queryIdx ].pt.y;
 scene2.push_back(aux2);
 
 } 
 
 Mat rvec, tvec, rmat;
 
rmat;
Mat cameraMatrix = (Mat_<float>(3,3) << 374.67,0,320.5,0,374.67,180.5,0,0,1);
 
374.67,0,320.5,0,374.67,180.5,0,0,1);
solvePnPRansac( obj3, scene2, cameraMatrix, noArray(), rvec, tvec);
 
tvec);
Rodrigues(rvec, rmat);
 
rmat);
std::vector<double> euler_angles (3);
 
(3);
std::cout << "rvec from solvePnPRansac: " << std::endl << rvec << std::endl;
 
std::endl;
std::cout << "rmat from solvePnPRansac: " << std::endl << rmat << std::endl;
 
euler_angles=get_Euler_angles(rmat);
 
std::endl;
euler_angles=get_Euler_angles(rmat);
std::cout << "euler angles from solvePnPRansac: " << std::endl << "[" << euler_angles[0] << " "<< euler_angles[1] << " " << euler_angles[2] << "]" << std::endl;
 
std::endl;
std::cout << "tvec from solvePnPRansac: " << std::endl << tvec << std::endl;
 
std::endl;
If I use two images as input I get the matches and a translation vector, but rotation vector is empty:
 
empty:
rvec from solvePnPRansac: 
 
[0;
 
0;
 
0]
 

[0;
0;
0]
rmat from solvePnPRansac: 
 
 [1, 0, 0;
 
0;
0, 1, 0;
 
0;
0, 0, 1]
 
1]
euler angles from solvePnPRansac: 
 
 [-0 0 0]
 
0]
tvec from solvePnPRansac: 
 
[-320.5000258050974;
 
-180.4999954623273;
 
374.6697010743459]
[-320.5000258050974;
-180.4999954623273;
374.6697010743459]