From 3ee0b896a4806cfcc0f10a3d4033646180276414 Mon Sep 17 00:00:00 2001
From: abn <adrien.bruneton@cea.fr>
Date: Wed, 27 Jun 2018 14:03:14 +0200
Subject: [PATCH] SegSegIntersector fix: fix eps comparison to detect seg/seg
 overlap

---
 .../Geometric2D/InterpKernelGeo2DEdgeLin.cxx  | 19 +++++++++++--------
 .../MEDCouplingIntersectTest.py               | 17 +++++++++++++++++
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/src/INTERP_KERNEL/Geometric2D/InterpKernelGeo2DEdgeLin.cxx b/src/INTERP_KERNEL/Geometric2D/InterpKernelGeo2DEdgeLin.cxx
index ed4eb1882..125ab5506 100644
--- a/src/INTERP_KERNEL/Geometric2D/InterpKernelGeo2DEdgeLin.cxx
+++ b/src/INTERP_KERNEL/Geometric2D/InterpKernelGeo2DEdgeLin.cxx
@@ -123,9 +123,10 @@ bool SegSegIntersector::areColinears() const
  * \param whereToFind specifies the box where final seek should be done. Essentially it is used for caracteristic reason.
  * \param colinearity returns if regarding QuadraticPlanarPrecision::getPrecision() ; e1 and e2 are colinears
  *                    If true 'this' is modified ! So this method be called once above all if true is returned for this parameter.
- * \param areOverlapped if colinearity if true, this parameter looks if e1 and e2 are overlapped.
+ * \param areOverlapped if colinearity if true, this parameter looks if e1 and e2 are overlapped, i.e. is they lie on the same line (= this is different from
+ * a true intersection, two segments can be in "overlap" mode, without intersecting)
  */
-void SegSegIntersector::areOverlappedOrOnlyColinears(const Bounds *whereToFind, bool& colinearity, bool& areOverlapped)
+void SegSegIntersector::areOverlappedOrOnlyColinears(const Bounds *whereToFind, bool& obviousNoIntersection, bool& areOverlapped)
 {
   double determinant=_matrix[0]*_matrix[3]-_matrix[1]*_matrix[2];
   Bounds b;
@@ -138,20 +139,22 @@ void SegSegIntersector::areOverlappedOrOnlyColinears(const Bounds *whereToFind,
   // [ABN] the 2 is not really justified, but the initial tests from Tony were written so closely to precision that I can't bother to change all of them ...
   if(fabs(determinant)>2.*dimChar*QuadraticPlanarPrecision::getPrecision())
     {
-      colinearity=false; areOverlapped=false;
+      obviousNoIntersection=false; areOverlapped=false;
       _matrix[0]/=determinant; _matrix[1]/=determinant; _matrix[2]/=determinant; _matrix[3]/=determinant;
     }
-  else
+  else  // colinear vectors
     {
-      colinearity=true;
-      //retrieving initial matrix
+      //retrieving initial matrix and shuffling it (will be used in getIntersectionsCharacteristicVal())
       double tmp=_matrix[0]; _matrix[0]=_matrix[3]; _matrix[3]=tmp;
       _matrix[1]=-_matrix[1]; _matrix[2]=-_matrix[2];
       //
-      double deno=sqrt(_matrix[0]*_matrix[0]+_matrix[1]*_matrix[1]);    // norm of e2
       double x=(*(_e1.getStartNode()))[0]-(*(_e2.getStartNode()))[0];
       double y=(*(_e1.getStartNode()))[1]-(*(_e2.getStartNode()))[1];   // (x,y) is the vector between the two start points of e1 and e2
-      areOverlapped=fabs((_matrix[1]*y+_matrix[0]*x)/deno)<QuadraticPlanarPrecision::getPrecision(); // test colinearity of (x,y) with e2
+      areOverlapped = fabs(_matrix[1]*y+_matrix[0]*x) < dimChar*QuadraticPlanarPrecision::getPrecision(); // test colinearity of (x,y) with e1
+
+      // explanation: if areOverlapped is true, we don't know yet if there will be an intersection (see meaning of areOverlapped in method doxy above)
+      // if areOverlapped is false, we have two colinear vectors, not lying on the same line, so we're sure there is no intersec
+      obviousNoIntersection = !areOverlapped;
     }
 }
 
diff --git a/src/MEDCoupling_Swig/MEDCouplingIntersectTest.py b/src/MEDCoupling_Swig/MEDCouplingIntersectTest.py
index 2bb2f8851..17acd21f9 100644
--- a/src/MEDCoupling_Swig/MEDCouplingIntersectTest.py
+++ b/src/MEDCoupling_Swig/MEDCouplingIntersectTest.py
@@ -1069,6 +1069,23 @@ class MEDCouplingIntersectTest(unittest.TestCase):
         self.assertTrue(m.getNodalConnectivityIndex().isEqual(DataArrayInt([0,13,20,27])))
         pass
 
+    def testSwig2Conformize2D6(self):
+        """ Was raising an internal error on the tiny cell #1. SegSegIntersector was faulty (eps misinterpreted)."""
+        eps=1.0e-6
+        mesh = MEDCouplingUMesh('Intersect2D', 2)
+        coo = DataArrayDouble([(-8.575398341058831,39.144034061751867),(-7.163839075265572,39.460696499553713),(-8.555240716524352,39.000452491656162),(-8.575381177420400,39.143911806168589),(-8.575389759239616,39.143972933960228),(-8.565310946972376,39.072182148912376),(-8.429007892596994,39.323429450193125),(-7.276475921428452,39.552916149667766),(-7.853580170499488,39.442382740946520),(-8.501337660834821,39.233025525494369),(-8.451698830704938,39.023021732647329),(-8.575293095466966,39.143931102458232),(-7.321160265208347,39.250835031152391),(-7.193377962393479,39.421292562742188),(-8.503477261299500,39.011771463728323),(-7.257269113800913,39.336063796947286),(-8.575337136449106,39.143921454338184),(-8.513495963085951,39.083476417552781),(-7.178608518829526,39.440994531147950),(-8.575345718262898,39.143982582105053),(-7.887252103212342,39.141010366774864),(-7.885555090015171,39.288688127112323),(-7.223911296170824,39.502221445493511)])
+        mesh.setCoords(coo)
+        c = DataArrayInt([32, 2, 3, 11, 10, 5, 16, 17, 14, 32, 3, 0, 11, 4, 19, 16, 32, 13, 12, 10, 11, 15, 20, 17, 21, 32, 7, 1, 13, 11, 0, 6, 22, 18, 21, 19, 9, 8])
+        cI = DataArrayInt([0, 9, 16, 25, 38])
+        mesh.setConnectivity(c, cI)     
+        
+        mesh.conformize2D(eps)  # internal error was here
+        
+        c2, cI2 = mesh.getNodalConnectivity().getValues(), mesh.getNodalConnectivityIndex().getValues()
+        self.assertEqual(c2, c.getValues())
+        self.assertEqual(cI2, cI.getValues())
+        pass
+
     def testSwig2Conformize3D1(self):
         """ Simple test where no edge merge is required, only face merging (first part of the algo) """
         mesh = MEDCouplingUMesh('merge', 3)
-- 
2.39.2