From 4d7ce375fc76a5ce51b244866e1f67b5621ef4e9 Mon Sep 17 00:00:00 2001
From: Vincent Rabaud <vrabaud@google.com>
Date: Mon, 8 Dec 2025 09:44:02 +0100
Subject: [PATCH] Increase minAreaRect accuracy

Just keep doubles all the way and avoid arithmetic with CV_PI/2
---
 modules/imgproc/src/rotcalipers.cpp    | 10 +++++-----
 modules/imgproc/test/test_convhull.cpp |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/modules/imgproc/src/rotcalipers.cpp b/modules/imgproc/src/rotcalipers.cpp
index d906258650..e28058b199 100644
--- a/modules/imgproc/src/rotcalipers.cpp
+++ b/modules/imgproc/src/rotcalipers.cpp
@@ -365,7 +365,7 @@ cv::RotatedRect cv::minAreaRect( InputArray _points )
     Mat hull;
     Point2f out[3];
     RotatedRect box;
-    box.angle = -(float)CV_PI / 2;  // default angle for box without rotation and single point
+    double angle = -CV_PI / 2;  // default angle for box without rotation and single point
 
     static const bool clockwise = false;
     convexHull(_points, hull, clockwise, true);
@@ -390,7 +390,7 @@ cv::RotatedRect cv::minAreaRect( InputArray _points )
         if (out[1].x == 0.f && out[1].y > 0.f)
             std::swap(box.size.width, box.size.height);
         else
-            box.angle += (float)atan2( (double)out[1].y, (double)out[1].x );
+            angle = -atan2( (double)out[1].x, (double)out[1].y );
     }
     else if( n == 2 )
     {
@@ -406,12 +406,12 @@ cv::RotatedRect cv::minAreaRect( InputArray _points )
         }
         else if (dy < 0)
         {
-            box.angle = (float)atan2( dy, dx );
+            angle = atan2( dy, dx );
             std::swap(box.size.width, box.size.height);
         }
         else if (dy > 0)
         {
-            box.angle += (float)atan2( dy, dx );
+            angle = -atan2( dx, dy );
         }
     }
     else
@@ -420,7 +420,7 @@ cv::RotatedRect cv::minAreaRect( InputArray _points )
             box.center = hpoints[0];
     }
 
-    box.angle = (float)(box.angle*180/CV_PI);
+    box.angle = (float)(angle*180/CV_PI);
     CV_DbgCheckGE(box.angle, -90.0f, "");
     CV_DbgCheckLT(box.angle, 0.0f, "");
     return box;
diff --git a/modules/imgproc/test/test_convhull.cpp b/modules/imgproc/test/test_convhull.cpp
index 774bee7af6..24c1604d2a 100644
--- a/modules/imgproc/test/test_convhull.cpp
+++ b/modules/imgproc/test/test_convhull.cpp
@@ -1279,7 +1279,7 @@ INSTANTIATE_TEST_CASE_P(Imgproc, minAreaRect_of_line,
         testing::Values(
             std::make_tuple(Point2f(10, 15), Point2f(10, 25), Point2f(10, 20), Size2f(10, 0), -90.f),
             std::make_tuple(Point2f(450, 500), Point2f(508, 500), Point2f(479, 500), Size2f(0, 58), -90.f),
-            std::make_tuple(Point2f(10, 20), Point2f(13, 16), Point2f(11.5, 18), Size2f(5, 0), -53.1301002f),
+            std::make_tuple(Point2f(10, 20), Point2f(13, 16), Point2f(11.5, 18), Size2f(5, 0), -53.1301041f),
             std::make_tuple(Point2f(9, 19), Point2f(4, 7), Point2f(6.5, 13), Size2f(0, 13), -22.6198654f)
         ));