From 78bd55c8df9bef7b87c4cdce029b805f58345fd5 Mon Sep 17 00:00:00 2001
From: Jim Zhou <jimzhou001@gmail.com>
Date: Fri, 11 Jan 2019 21:58:47 +0800
Subject: [PATCH] Merge pull request #13601 from JimZhou-001:JimZhou-001

* Fix the bug in case determinant of rotation matrix is -1

* calib3d(test): check det(R) == 1
---
 modules/calib3d/src/homography_decomp.cpp       |  8 +++++++
 modules/calib3d/test/test_homography_decomp.cpp | 32 +++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/modules/calib3d/src/homography_decomp.cpp b/modules/calib3d/src/homography_decomp.cpp
index fea8882..3bfb62e 100644
--- a/modules/calib3d/src/homography_decomp.cpp
+++ b/modules/calib3d/src/homography_decomp.cpp
@@ -185,6 +185,10 @@ bool HomographyDecompZhang::findMotionFrom_tstar_n(const cv::Vec3d& tstar, const
     temp(1, 1) += 1.0;
     temp(2, 2) += 1.0;
     motion.R = getHnorm() * temp.inv();
+    if (cv::determinant(motion.R) < 0)
+    {
+        motion.R *= -1;
+    }
     motion.t = motion.R * tstar;
     motion.n = n;
     return passesSameSideOfPlaneConstraint(motion);
@@ -312,6 +316,10 @@ void HomographyDecompInria::findRmatFrom_tstar_n(const cv::Vec3d& tstar, const c
               0.0, 0.0, 1.0);
 
     R = getHnorm() * (I - (2/v) * tstar_m * n_m.t() );
+    if (cv::determinant(R) < 0)
+    {
+        R *= -1;
+    }
 }
 
 void HomographyDecompInria::decompose(std::vector<CameraMotion>& camMotions)
diff --git a/modules/calib3d/test/test_homography_decomp.cpp b/modules/calib3d/test/test_homography_decomp.cpp
index 45f5ae6..9ddc0e9 100644
--- a/modules/calib3d/test/test_homography_decomp.cpp
+++ b/modules/calib3d/test/test_homography_decomp.cpp
@@ -134,4 +134,36 @@ private:
 
 TEST(Calib3d_DecomposeHomography, regression) { CV_HomographyDecompTest test; test.safe_run(); }
 
+
+TEST(Calib3d_DecomposeHomography, issue_4978)
+{
+    Matx33d K(
+        1.0,   0.0,    0.0,
+        0.0,   1.0,    0.0,
+        0.0,   0.0,    1.0
+    );
+
+    Matx33d H(
+        -0.102896, 0.270191,   -0.0031153,
+        0.0406387, 1.19569,    -0.0120456,
+        0.445351,  0.0410889,  1
+    );
+
+    vector<Mat> rotations;
+    vector<Mat> translations;
+    vector<Mat> normals;
+
+    decomposeHomographyMat(H, K, rotations, translations, normals);
+
+    ASSERT_GT(rotations.size(), (size_t)0u);
+    for (size_t i = 0; i < rotations.size(); i++)
+    {
+        // check: det(R) = 1
+        EXPECT_TRUE(std::fabs(cv::determinant(rotations[i]) - 1.0) < 0.01)
+            << "R: det=" << cv::determinant(rotations[0]) << std::endl << rotations[i] << std::endl
+            << "T:" << std::endl << translations[i] << std::endl;
+    }
+}
+
+
 }} // namespace
-- 
2.7.4