From 0726f206947c230d06b428b5e158464bd196492f Mon Sep 17 00:00:00 2001
From: Jon Jenssen <jon@soundsoft.no>
Date: Thu, 30 Apr 2026 16:33:04 +0200
Subject: [PATCH] Protect flattening code against polylines with a single point

---
 .../Intersections/RivSectionFlattener.cpp     | 11 ++++++--
 .../RimExtrudedCurveIntersection.cpp          | 25 +++++++++++++------
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/ApplicationLibCode/ModelVisualization/Intersections/RivSectionFlattener.cpp b/ApplicationLibCode/ModelVisualization/Intersections/RivSectionFlattener.cpp
index 6e86683542..686ef9aa5b 100644
--- a/ApplicationLibCode/ModelVisualization/Intersections/RivSectionFlattener.cpp
+++ b/ApplicationLibCode/ModelVisualization/Intersections/RivSectionFlattener.cpp
@@ -55,8 +55,15 @@ std::vector<cvf::Mat4d> RivSectionFlattener::calculateFlatteningCSsForPolyline(
                                                                                 cvf::Vec3d*                    endOffset )
 {
     CVF_ASSERT( endOffset );
-    size_t pointCount = polyLine.size();
-    CVF_ASSERT( pointCount > 1 );
+    const size_t pointCount = polyLine.size();
+    if ( pointCount == 0 ) return {};
+    // If only one point, return identity matrix, as we can't calculate a direction
+    if ( pointCount == 1 )
+    {
+        // trigger assert in debug builds, as this should not happen, but return something valid in release builds
+        CVF_TIGHT_ASSERT( false );
+        return { cvf::Mat4d() };
+    }
 
     std::vector<cvf::Mat4d> segmentTransforms;
     segmentTransforms.reserve( pointCount );
diff --git a/ApplicationLibCode/ProjectDataModel/Intersections/RimExtrudedCurveIntersection.cpp b/ApplicationLibCode/ProjectDataModel/Intersections/RimExtrudedCurveIntersection.cpp
index 5200554469..480720ada4 100644
--- a/ApplicationLibCode/ProjectDataModel/Intersections/RimExtrudedCurveIntersection.cpp
+++ b/ApplicationLibCode/ProjectDataModel/Intersections/RimExtrudedCurveIntersection.cpp
@@ -848,6 +848,16 @@ std::vector<std::vector<cvf::Vec3d>> RimExtrudedCurveIntersection::polyLines( cv
         lines.push_back( m_twoAzimuthPoints );
     }
 
+    // remove all line segments with less than 2 points
+    std::vector<std::vector<cvf::Vec3d>> filteredLines;
+    for ( auto l : lines )
+    {
+        if ( l.size() > 1 )
+        {
+            filteredLines.push_back( l );
+        }
+    }
+
     if ( type() == CrossSectionEnum::CS_WELL_PATH || type() == CrossSectionEnum::CS_SIMULATION_WELL )
     {
         if ( type() == CrossSectionEnum::CS_SIMULATION_WELL && m_simulationWell() )
@@ -856,31 +866,32 @@ std::vector<std::vector<cvf::Vec3d>> RimExtrudedCurveIntersection::polyLines( cv
 
             m_simulationWell->wellHeadTopBottomPosition( -1, &top, &bottom );
 
-            for ( std::vector<cvf::Vec3d>& polyLine : lines )
+            for ( std::vector<cvf::Vec3d>& polyLine : filteredLines )
             {
                 polyLine.insert( polyLine.begin(), top );
             }
         }
 
-        for ( std::vector<cvf::Vec3d>& polyLine : lines )
+        for ( std::vector<cvf::Vec3d>& polyLine : filteredLines )
         {
             addExtents( polyLine );
         }
 
-        if ( flattenedPolylineStartPoint && !lines.empty() && lines[0].size() > 1 )
+        if ( flattenedPolylineStartPoint && !filteredLines.empty() && filteredLines[0].size() > 1 )
         {
             ( *flattenedPolylineStartPoint )[0] = horizontalProjectedLengthAlongWellPathToClipPoint - m_extentLength;
-            ( *flattenedPolylineStartPoint )[2] = lines[0][1].z(); // Depth of first point in first polyline
+            ( *flattenedPolylineStartPoint )[2] = filteredLines[0][1].z(); // Depth of first point in first polyline
         }
     }
     else
     {
-        if ( flattenedPolylineStartPoint && !lines.empty() && !( lines[0] ).empty() )
+        if ( flattenedPolylineStartPoint && !filteredLines.empty() && !( filteredLines[0] ).empty() )
         {
-            ( *flattenedPolylineStartPoint )[2] = lines[0][0].z(); // Depth of first point in first polyline
+            ( *flattenedPolylineStartPoint )[2] = filteredLines[0][0].z(); // Depth of first point in first polyline
         }
     }
-    return lines;
+
+    return filteredLines;
 }
 
 //--------------------------------------------------------------------------------------------------