diff --git a/ArcSpecial.cpp b/ArcSpecial.cpp
index bc489e1..7c147c9 100644
--- a/ArcSpecial.cpp
+++ b/ArcSpecial.cpp
@@ -77,8 +77,8 @@ GetArc2PVN( const Point3d& ptStart, const Point3d& ptEnd, const Vector3d& vtDirS
 
   // calcolo arco non riuscito, verifico se retta va bene
    Vector3d vtDiff = ptEnd - ptStart ;
-   // verifico se i punti sono allineati con la direzione e nel giusto verso
-   if ( ( vtDiff ^ vtDirS).IsSmall()  &&  vtDiff * vtDirS > EPS_SMALL) {
+   // verifico se i punti sono allineati con la direzione e nel giusto verso nel piano perpendicolare a vtN
+   if ( abs( ( vtDiff ^ vtDirS) * vtN) < EPS_SMALL  &&  vtDiff * vtDirS > EPS_SMALL) {
      // creo l'oggetto retta
       ICurveLine* pLine = CreateCurveLine() ;
       if ( pLine == nullptr)
diff --git a/CurveComposite.cpp b/CurveComposite.cpp
index 73bdbb1..a956de0 100644
--- a/CurveComposite.cpp
+++ b/CurveComposite.cpp
@@ -2817,3 +2817,44 @@ CurveComposite::RemoveUndercutOnY( double dLinTol, double dAngTolDeg)
    Clear() ;
    return AddCurve( Release( pOutLoop)) ;
 }
+
+//----------------------------------------------------------------------------
+bool
+CurveComposite::IsOneCircle( Point3d& ptCen, Vector3d& vtN, double& dRad, bool& bCCW) const
+{
+  // deve essere una sola entità
+   if ( GetCurveCount() != 1)
+      return false ;
+  // deve essere un arco di circonferenza completo
+   const CurveArc* pArc = GetBasicCurveArc( GetFirstCurve()) ;
+   if ( pArc == nullptr  ||  ! pArc->IsACircle())
+      return false ;
+  // assegno i parametri
+   ptCen = pArc->GetCenter() ;
+   vtN = pArc->GetNormVersor() ;
+   dRad = pArc->GetRadius() ;
+   bCCW = ( pArc->GetAngCenter() > 0) ;
+   return true ;
+}
+
+//----------------------------------------------------------------------------
+bool
+CurveComposite::IsACircle( double dLinTol, Point3d& ptCen, Vector3d& vtN, double& dRad, bool& bCCW) const
+{
+  // deve essere chiusa
+   if ( ! IsClosed())
+      return false ;
+
+  // se è formata da una sola entità arco che è una circonferenza
+   if ( IsOneCircle( ptCen, vtN, dRad, bCCW))
+      return true ;
+
+  // provo ad approssimarla con archi e verifico se si riduce ad una circonferenza
+   PolyArc PA ;
+   if ( ! ApproxWithArcs( dLinTol, ANG_TOL_STD_DEG, PA))
+      return false ;
+   CurveComposite CrvTemp ;
+   if ( ! CrvTemp.FromPolyArc( PA)  ||  ! CrvTemp.MergeCurves( dLinTol, ANG_TOL_STD_DEG))
+      return false ;
+   return CrvTemp.IsOneCircle( ptCen, vtN, dRad, bCCW) ;
+}
diff --git a/CurveComposite.h b/CurveComposite.h
index 52c4606..3966b84 100644
--- a/CurveComposite.h
+++ b/CurveComposite.h
@@ -151,6 +151,7 @@ class CurveComposite : public ICurveComposite, public IGeoObjRW
       bool ArcsBezierCurvesToArcsPerpExtr( double dLinTol, double dAngTolDeg) override ;
       bool MergeCurves( double dLinTol, double dAngTolDeg, bool bStartEnd = true) override ;
       bool RemoveUndercutOnY( double dLinTol, double dAngTolDeg) override ;
+      bool IsACircle( double dLinTol, Point3d& ptCen, Vector3d& vtN, double& dRad, bool& bCCW) const override ;
 
    public :                      // IGeoObjRW
       virtual int GetNgeId( void) const ;
@@ -176,6 +177,7 @@ class CurveComposite : public ICurveComposite, public IGeoObjRW
       bool GetIndSCurveAndLocPar( double dU, Side nS, int& nSCrv, double& dLocU) const ;
       bool SimpleOffsetXY( double dDist, int nType = OFF_FILLET) ;
       bool MergeTwoCurves( ICurve* pCrvP, ICurve* pCrvC, double& dCurrLinTol, double dAngTolDeg) ;
+      bool IsOneCircle( Point3d& ptCen, Vector3d& vtN, double& dRad, bool& bCCW) const ;
 
    private :
       enum Status { ERR = 0, OK = 1, TO_VERIFY = 2} ;