From c69245da1f4f37097fe22501023552ac3eb686f5 Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.a.alekhin@gmail.com>
Date: Thu, 3 Oct 2019 20:45:43 +0000
Subject: [PATCH] imgproc: fix fitLine() implementation

- update optimal solutions on each iteration
---
 .../imgproc/misc/java/test/ImgprocTest.java   |  2 +-
 modules/imgproc/src/linefit.cpp               | 19 +++++++---
 modules/imgproc/test/test_convhull.cpp        | 35 +++++++++++++++++++
 3 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/modules/imgproc/misc/java/test/ImgprocTest.java b/modules/imgproc/misc/java/test/ImgprocTest.java
index ca23ee35b3..52da455993 100644
--- a/modules/imgproc/misc/java/test/ImgprocTest.java
+++ b/modules/imgproc/misc/java/test/ImgprocTest.java
@@ -807,7 +807,7 @@ public class ImgprocTest extends OpenCVTestCase {
         points.put(0, 0, 0, 0, 2, 3, 3, 4, 5, 8);
 
         Mat linePoints = new Mat(4, 1, CvType.CV_32FC1);
-        linePoints.put(0, 0, 0.53196341, 0.84676737, 2.496531, 3.7467217);
+        linePoints.put(0, 0, 0.53198653, 0.84675282, 2.5, 3.75);
 
         Imgproc.fitLine(points, dst, Imgproc.CV_DIST_L12, 0, 0.01, 0.01);
 
diff --git a/modules/imgproc/src/linefit.cpp b/modules/imgproc/src/linefit.cpp
index 1abde1e0d1..97e0d2961a 100644
--- a/modules/imgproc/src/linefit.cpp
+++ b/modules/imgproc/src/linefit.cpp
@@ -408,8 +408,14 @@ static void fitLine2D( const Point2f * points, int count, int dist,
             }
             /* calculate distances */
             err = calcDist2D( points, count, _line, r );
-            if( err < EPS )
-                break;
+
+            if (err < min_err)
+            {
+                min_err = err;
+                memcpy(line, _line, 4 * sizeof(line[0]));
+                if (err < EPS)
+                    break;
+            }
 
             /* calculate weights */
             if( calc_weights )
@@ -550,8 +556,13 @@ static void fitLine3D( Point3f * points, int count, int dist,
             }
             /* calculate distances */
             err = calcDist3D( points, count, _line, r );
-            //if( err < FLT_EPSILON*count )
-            //    break;
+            if (err < min_err)
+            {
+                min_err = err;
+                memcpy(line, _line, 6 * sizeof(line[0]));
+                if (err < EPS)
+                    break;
+            }
 
             /* calculate weights */
             if( calc_weights )
diff --git a/modules/imgproc/test/test_convhull.cpp b/modules/imgproc/test/test_convhull.cpp
index 3f82e04524..3f12140328 100644
--- a/modules/imgproc/test/test_convhull.cpp
+++ b/modules/imgproc/test/test_convhull.cpp
@@ -1609,6 +1609,8 @@ int CV_FitLineTest::validate_test_results( int test_case_idx )
     int k, max_k = 0;
     double vec_diff = 0, t;
 
+    //std::cout << dims << " " << Mat(1, dims*2, CV_32FC1, line.data()) << " " << Mat(1, dims, CV_32FC1, line0.data()) << std::endl;
+
     for( k = 0; k < dims*2; k++ )
     {
         if( cvIsNaN(line[k]) || cvIsInf(line[k]) )
@@ -2038,5 +2040,38 @@ INSTANTIATE_TEST_CASE_P(Imgproc, ConvexityDefects_regression_5908,
                 testing::Values(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
         ));
 
+TEST(Imgproc_FitLine, regression_15083)
+{
+    int points2i_[] = {
+        432, 654,
+        370, 656,
+        390, 656,
+        410, 656,
+        348, 658
+    };
+    Mat points(5, 1, CV_32SC2, points2i_);
+
+    Vec4f lineParam;
+    fitLine(points, lineParam, DIST_L1, 0, 0.01, 0.01);
+    EXPECT_GE(fabs(lineParam[0]), fabs(lineParam[1]) * 4) << lineParam;
+}
+
+TEST(Imgproc_FitLine, regression_4903)
+{
+    float points2f_[] = {
+        1224.0, 576.0,
+        1234.0, 683.0,
+        1215.0, 471.0,
+        1184.0, 137.0,
+        1079.0, 377.0,
+        1239.0, 788.0,
+    };
+    Mat points(6, 1, CV_32FC2, points2f_);
+
+    Vec4f lineParam;
+    fitLine(points, lineParam, DIST_WELSCH, 0, 0.01, 0.01);
+    EXPECT_GE(fabs(lineParam[1]), fabs(lineParam[0]) * 4) << lineParam;
+}
+
 }} // namespace
 /* End of file. */