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Merge pull request #17816 from vpisarev:essential_2cameras

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* add findEssentialMat for two different cameras

* added smoke test for the newly added variant of findEssentialMatrix

Co-authored-by: tompollok <tom.pollok@gmail.com>
pull/17992/head
Vadim Pisarevsky 4 years ago committed by GitHub
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commit a2f7ef9d21
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3 changed files with 89 additions and 2 deletions
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  1. 51
      modules/calib3d/include/opencv2/calib3d.hpp
  2. 29
      modules/calib3d/src/five-point.cpp
  3. 11
      modules/calib3d/test/test_cameracalibration.cpp

51
modules/calib3d/include/opencv2/calib3d.hpp
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@ -2522,6 +2522,57 @@ CV_EXPORTS_W Mat findEssentialMat( InputArray points1, InputArray points2,
int method = RANSAC, double prob = 0.999,
double threshold = 1.0, OutputArray mask = noArray() );
/** @brief Calculates an essential matrix from the corresponding points in two images from potentially two different cameras.
@param points1 Array of N (N \>= 5) 2D points from the first image. The point coordinates should
be floating-point (single or double precision).
@param points2 Array of the second image points of the same size and format as points1 .
@param cameraMatrix1 Camera matrix \f$K = \vecthreethree{f_x}{0}{c_x}{0}{f_y}{c_y}{0}{0}{1}\f$ .
Note that this function assumes that points1 and points2 are feature points from cameras with the
same camera matrix. If this assumption does not hold for your use case, use
`undistortPoints()` with `P = cv::NoArray()` for both cameras to transform image points
to normalized image coordinates, which are valid for the identity camera matrix. When
passing these coordinates, pass the identity matrix for this parameter.
@param cameraMatrix2 Camera matrix \f$K = \vecthreethree{f_x}{0}{c_x}{0}{f_y}{c_y}{0}{0}{1}\f$ .
Note that this function assumes that points1 and points2 are feature points from cameras with the
same camera matrix. If this assumption does not hold for your use case, use
`undistortPoints()` with `P = cv::NoArray()` for both cameras to transform image points
to normalized image coordinates, which are valid for the identity camera matrix. When
passing these coordinates, pass the identity matrix for this parameter.
@param distCoeffs1 Input vector of distortion coefficients
\f$(k_1, k_2, p_1, p_2[, k_3[, k_4, k_5, k_6[, s_1, s_2, s_3, s_4[, \tau_x, \tau_y]]]])\f$
of 4, 5, 8, 12 or 14 elements. If the vector is NULL/empty, the zero distortion coefficients are assumed.
@param distCoeffs2 Input vector of distortion coefficients
\f$(k_1, k_2, p_1, p_2[, k_3[, k_4, k_5, k_6[, s_1, s_2, s_3, s_4[, \tau_x, \tau_y]]]])\f$
of 4, 5, 8, 12 or 14 elements. If the vector is NULL/empty, the zero distortion coefficients are assumed.
@param method Method for computing an essential matrix.
- **RANSAC** for the RANSAC algorithm.
- **LMEDS** for the LMedS algorithm.
@param prob Parameter used for the RANSAC or LMedS methods only. It specifies a desirable level of
confidence (probability) that the estimated matrix is correct.
@param threshold Parameter used for RANSAC. It is the maximum distance from a point to an epipolar
line in pixels, beyond which the point is considered an outlier and is not used for computing the
final fundamental matrix. It can be set to something like 1-3, depending on the accuracy of the
point localization, image resolution, and the image noise.
@param mask Output array of N elements, every element of which is set to 0 for outliers and to 1
for the other points. The array is computed only in the RANSAC and LMedS methods.
This function estimates essential matrix based on the five-point algorithm solver in @cite Nister03 .
@cite SteweniusCFS is also a related. The epipolar geometry is described by the following equation:
\f[[p_2; 1]^T K^{-T} E K^{-1} [p_1; 1] = 0\f]
where \f$E\f$ is an essential matrix, \f$p_1\f$ and \f$p_2\f$ are corresponding points in the first and the
second images, respectively. The result of this function may be passed further to
decomposeEssentialMat or recoverPose to recover the relative pose between cameras.
*/
CV_EXPORTS_W Mat findEssentialMat( InputArray points1, InputArray points2,
InputArray cameraMatrix1, InputArray distCoeffs1,
InputArray cameraMatrix2, InputArray distCoeffs2,
int method = RANSAC,
double prob = 0.999, double threshold = 1.0,
OutputArray mask = noArray() );
/** @brief Decompose an essential matrix to possible rotations and translation.
@param E The input essential matrix.

29
modules/calib3d/src/five-point.cpp
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@ -458,6 +458,35 @@ cv::Mat cv::findEssentialMat( InputArray _points1, InputArray _points2, double f
return cv::findEssentialMat(_points1, _points2, cameraMatrix, method, prob, threshold, _mask);
}
cv::Mat cv::findEssentialMat( InputArray _points1, InputArray _points2,
InputArray cameraMatrix1, InputArray distCoeffs1,
InputArray cameraMatrix2, InputArray distCoeffs2,
int method, double prob, double threshold, OutputArray _mask)
{
CV_INSTRUMENT_REGION();
// Undistort image points, bring them to 3x3 identity "camera matrix"
Mat _pointsUntistorted1, _pointsUntistorted2;
undistortPoints(_points1, _pointsUntistorted1, cameraMatrix1, distCoeffs1);
undistortPoints(_points2, _pointsUntistorted2, cameraMatrix2, distCoeffs2);
// Scale the points back. We use "arithmetic mean" between the supplied two camera matrices.
// Thanks to such 2-stage procedure RANSAC threshold still makes sense, because the undistorted
// and rescaled points have a similar value range to the original ones.
Mat cm1 = cameraMatrix1.getMat(), cm2 = cameraMatrix2.getMat(), cm0;
Mat(cm1 + cm2).convertTo(cm0, CV_64F, 0.5);
CV_Assert(cm0.rows == 3 && cm0.cols == 3);
CV_Assert(std::abs(cm0.at<double>(2, 0)) < 1e-3 &&
std::abs(cm0.at<double>(2, 1)) < 1e-3 &&
std::abs(cm0.at<double>(2, 2) - 1.) < 1e-3);
Mat affine = cm0.rowRange(0, 2);
transform(_pointsUntistorted1, _pointsUntistorted1, affine);
transform(_pointsUntistorted2, _pointsUntistorted2, affine);
return findEssentialMat(_pointsUntistorted1, _pointsUntistorted2, cm0, method, prob, threshold, _mask);
}
int cv::recoverPose( InputArray E, InputArray _points1, InputArray _points2,
InputArray _cameraMatrix, OutputArray _R, OutputArray _t, double distanceThresh,
InputOutputArray _mask, OutputArray triangulatedPoints)

11
modules/calib3d/test/test_cameracalibration.cpp
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@ -2142,6 +2142,7 @@ TEST(CV_RecoverPoseTest, regression_15341)
// camera matrix with both focal lengths = 1, and principal point = (0, 0)
const Mat cameraMatrix = Mat::eye(3, 3, CV_64F);
const Mat zeroDistCoeffs = Mat::zeros(1, 5, CV_64F);
int Inliers = 0;
@ -2156,8 +2157,11 @@ TEST(CV_RecoverPoseTest, regression_15341)
vector<Point2f> points2(_points2);
// Estimation of fundamental matrix using the RANSAC algorithm
Mat E, R, t;
Mat E, E2, R, t;
E = findEssentialMat(points1, points2, cameraMatrix, RANSAC, 0.999, 1.0, mask);
E2 = findEssentialMat(points1, points2, cameraMatrix, zeroDistCoeffs, cameraMatrix, zeroDistCoeffs, RANSAC, 0.999, 1.0, mask);
EXPECT_LT(cv::norm(E, E2, NORM_INF), 1e-4) <<
"Two big difference between the same essential matrices computed using different functions, testcase " << testcase;
EXPECT_EQ(0, (int)mask[13]) << "Detecting outliers in function findEssentialMat failed, testcase " << testcase;
points2[12] = Point2f(0.0f, 0.0f); // provoke another outlier detection for recover Pose
Inliers = recoverPose(E, points1, points2, cameraMatrix, R, t, mask);
@ -2180,8 +2184,11 @@ TEST(CV_RecoverPoseTest, regression_15341)
}
// Estimation of fundamental matrix using the RANSAC algorithm
Mat E, R, t;
Mat E, E2, R, t;
E = findEssentialMat(points1, points2, cameraMatrix, RANSAC, 0.999, 1.0, mask);
E2 = findEssentialMat(points1, points2, cameraMatrix, zeroDistCoeffs, cameraMatrix, zeroDistCoeffs, RANSAC, 0.999, 1.0, mask);
EXPECT_LT(cv::norm(E, E2, NORM_INF), 1e-4) <<
"Two big difference between the same essential matrices computed using different functions, testcase " << testcase;
EXPECT_EQ(0, (int)mask.at<unsigned char>(13)) << "Detecting outliers in function findEssentialMat failed, testcase " << testcase;
points2.at<Point2f>(12) = Point2f(0.0f, 0.0f); // provoke an outlier detection
Inliers = recoverPose(E, points1, points2, cameraMatrix, R, t, mask);

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