diff --git a/PolyLine.cpp b/PolyLine.cpp
index 755b064..4678ce9 100644
--- a/PolyLine.cpp
+++ b/PolyLine.cpp
@@ -587,18 +587,29 @@ PolyLine::IsClosedAndFlat( Plane3d& plPlane, double& dArea, double dToler) const
   // Test if closed
    if ( ! IsClosed())
       return false ;
-  // Compute a representative plane for the polygon
    Point3d ptP ;
+  // Calcolo il centro (per minimizzare gli errori nelle successive operazioni)
+   Point3d ptCen = ORIG ;
+   int nCount = 0 ;
+   for ( bool bFound = GetFirstPoint( ptP) ; bFound ; bFound = GetNextPoint( ptP)) {
+      ptCen += ptP ;
+      ++ nCount ;
+   }  
+   ptCen /= nCount ;
+   Vector3d vtMove = ptCen - ORIG ;
+  // Compute a representative plane for the polygon (faccio il calcolo nel centro e poi traslo al contrario il piano)
    PolygonPlane PolyPlane ;
    for ( bool bFound = GetFirstPoint( ptP) ; bFound ; bFound = GetNextPoint( ptP))
-      PolyPlane.AddPoint( ptP) ;
+      PolyPlane.AddPoint( ptP - vtMove) ;
    if ( ! PolyPlane.GetPlane( plPlane)  ||  ! PolyPlane.GetArea( dArea)) {
       dArea = 0 ;
       return IsFlat( plPlane, dToler) ;
    }
+   plPlane.Translate( vtMove) ;
+  // Sistemo il piano per l'offset utilizzato
   // Test each vertex to see if it is farther from plane than allowed max distance
    for ( bool bFound = GetFirstPoint( ptP) ; bFound ; bFound = GetNextPoint( ptP)) {
-      double dDist = ( ( ptP - ORIG) * plPlane.GetVersN()) - plPlane.GetDist() ;
+      double dDist = DistPointPlane( ptP, plPlane) ;
       if ( abs( dDist) > dToler)
          return false ;
    }
diff --git a/SurfFlatRegion.cpp b/SurfFlatRegion.cpp
index 0027f7c..41b74cb 100644
--- a/SurfFlatRegion.cpp
+++ b/SurfFlatRegion.cpp
@@ -109,18 +109,25 @@ SurfFlatRegion::AddExtLoop( ICurve* pCrv)
    if ( ! AdjustLoops( Release( pMyCrv), CrvLst, true))
       return false ;
   // aggiungo le singole curve
+   int nExtAdded = 0 ;
    bool bOk = true ;
    for ( auto& pSingCrv : CrvLst) {
-      if ( ! AddSimpleExtLoop( pSingCrv))
+      bool bAdded = false ;
+      if ( AddSimpleExtLoop( pSingCrv, bAdded))
+         ++ nExtAdded ;
+      else
          bOk = false ;
+
    }
-   return bOk ;
+   return ( bOk  &&  nExtAdded > 0) ;
 }
 
 //----------------------------------------------------------------------------
 bool
-SurfFlatRegion::AddSimpleExtLoop( ICurve* pCrv)
+SurfFlatRegion::AddSimpleExtLoop( ICurve* pCrv, bool& bAdded)
 {
+  // default
+   bAdded = false ;
   // acquisisco la curva
    PtrOwner<ICurve> pMyCrv( pCrv) ;
    if ( IsNull( pMyCrv))
@@ -133,6 +140,8 @@ SurfFlatRegion::AddSimpleExtLoop( ICurve* pCrv)
    Plane3d plPlane ;
    if ( ! pMyCrv->GetArea( plPlane, dArea))
       return false ;
+   if ( dArea < SQ_EPS_SMALL)
+      return true ;
   // se sto costruendo il primo chunk
    if ( m_vExtInd.size() == 0) {
      // assegno il riferimento intrinseco
@@ -198,6 +207,7 @@ SurfFlatRegion::AddSimpleExtLoop( ICurve* pCrv)
    m_OGrMgr.Reset() ;
   // imposto ricalcolo Voronoi
    ResetVoronoiObject() ;
+   bAdded = true ;
    return true ;
 }
 
diff --git a/SurfFlatRegion.h b/SurfFlatRegion.h
index c1198e8..d257fce 100644
--- a/SurfFlatRegion.h
+++ b/SurfFlatRegion.h
@@ -142,7 +142,7 @@ class SurfFlatRegion : public ISurfFlatRegion, public IGeoObjRW
 
    private :
       bool CopyFrom( const SurfFlatRegion& clSrc) ;
-      bool AddSimpleExtLoop( ICurve* pCrv) ;
+      bool AddSimpleExtLoop( ICurve* pCrv, bool& bAdded) ;
       bool MyAddExtLoop( ICurve* pCrv) ;
       bool AddSimpleIntLoop( ICurve* pCrv) ;
       bool MyAddIntLoop( ICurve* pCrv, int nChunk) ;