From c548c4a12bd34c4f6f33b3ba77aba01dc429cb77 Mon Sep 17 00:00:00 2001
From: Magne Sjaastad <magne.sjaastad@ceetronsolutions.com>
Date: Mon, 25 May 2020 20:43:59 +0200
Subject: [PATCH] #5899 Fracture: Use robust way to find diff between two
 angles

---
 .../Completions/RimFracture.cpp               | 23 +++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/ApplicationCode/ProjectDataModel/Completions/RimFracture.cpp b/ApplicationCode/ProjectDataModel/Completions/RimFracture.cpp
index edaa39c45e..ec79ce4c12 100644
--- a/ApplicationCode/ProjectDataModel/Completions/RimFracture.cpp
+++ b/ApplicationCode/ProjectDataModel/Completions/RimFracture.cpp
@@ -381,13 +381,29 @@ double RimFracture::endMD() const
     }
 }
 
+//--------------------------------------------------------------------------------------------------
+/// https://stackoverflow.com/a/52432897
+//--------------------------------------------------------------------------------------------------
+double getAbsoluteDiff2Angles( const double x, const double y, const double c )
+{
+    // c can be PI (for radians) or 180.0 (for degrees);
+    return c - fabs( fmod( fabs( x - y ), 2 * c ) - c );
+}
+
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
 double RimFracture::wellFractureAzimuthDiff() const
 {
-    double wellDifference = fabs( wellAzimuthAtFracturePosition() - m_azimuth );
-    return wellDifference;
+    // Compute the relative difference between two lines
+    // See https://github.com/OPM/ResInsight/issues/5899
+
+    double angle1 = wellAzimuthAtFracturePosition();
+    double angle2 = m_azimuth;
+
+    double smallestDiffDegrees = getAbsoluteDiff2Angles( angle1, angle2, 180.0 );
+
+    return smallestDiffDegrees;
 }
 
 //--------------------------------------------------------------------------------------------------
@@ -399,6 +415,9 @@ QString RimFracture::wellFractureAzimuthDiffText() const
     return QString::number( wellDifference, 'f', 2 );
 }
 
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
 QString RimFracture::wellAzimuthAtFracturePositionText() const
 {
     double wellAzimuth = wellAzimuthAtFracturePosition();