diff --git a/EGkGeoConst.h b/EGkGeoConst.h
index ce11f4c..e604579 100644
--- a/EGkGeoConst.h
+++ b/EGkGeoConst.h
@@ -19,9 +19,10 @@
 const double ONEMM =    1.0 ;
 const double ONEINCH = 25.4 ;
 
-// epsilon per lunghezze e versori
+// epsilon per lunghezze, versori e parametri
 const double EPS_SMALL = 1e-3 ;
 const double EPS_ZERO  = 1e-7 ;
+const double EPS_PARAM = 1e-7 ;
 
 // infinito per lunghezze
 const double INFINITO = 1e10 ;
diff --git a/EGkPolyLine.h b/EGkPolyLine.h
index 8a098d8..b91f375 100644
--- a/EGkPolyLine.h
+++ b/EGkPolyLine.h
@@ -42,25 +42,25 @@ class PolyLine
       EGK_EXPORT int  GetPointNbr( void) const
                         { return m_nCount ; }
       EGK_EXPORT bool GetFirstUPoint( double* pdPar, Point3d* pptP) const ;
-      EGK_EXPORT bool GetNextUPoint( double* pdPar, Point3d* pptP) const ;
+      EGK_EXPORT bool GetNextUPoint( double* pdPar, Point3d* pptP, bool bNotLast = false) const ;
       EGK_EXPORT bool GetFirstU( double& dPar) const
                         { return GetFirstUPoint( &dPar, nullptr) ; }
-      EGK_EXPORT bool GetNextU( double& dPar) const
-                        { return GetNextUPoint( &dPar, nullptr) ; }
+      EGK_EXPORT bool GetNextU( double& dPar, bool bNotLast = false) const
+                        { return GetNextUPoint( &dPar, nullptr, bNotLast) ; }
       EGK_EXPORT bool GetFirstPoint( Point3d& ptP) const
                         { return GetFirstUPoint( nullptr, &ptP) ; }
-      EGK_EXPORT bool GetNextPoint( Point3d& ptP) const
-                        { return GetNextUPoint( nullptr, &ptP) ; }
+      EGK_EXPORT bool GetNextPoint( Point3d& ptP, bool bNotLast = false) const
+                        { return GetNextUPoint( nullptr, &ptP, bNotLast) ; }
       EGK_EXPORT bool GetLastUPoint( double* pdPar, Point3d* pptP) const ;
-      EGK_EXPORT bool GetPrevUPoint( double* pdPar, Point3d* pptP) const ;
+      EGK_EXPORT bool GetPrevUPoint( double* pdPar, Point3d* pptP, bool bNotFirst = false) const ;
       EGK_EXPORT bool GetLastU( double& dPar) const
                         { return GetLastUPoint( &dPar, nullptr) ; }
-      EGK_EXPORT bool GetPrevU( double& dPar) const
-                        { return GetPrevUPoint( &dPar, nullptr) ; }
+      EGK_EXPORT bool GetPrevU( double& dPar, bool bNotFirst = false) const
+                        { return GetPrevUPoint( &dPar, nullptr, bNotFirst) ; }
       EGK_EXPORT bool GetLastPoint( Point3d& ptP) const
                         { return GetLastUPoint( nullptr, &ptP) ; }
-      EGK_EXPORT bool GetPrevPoint( Point3d& ptP) const
-                        { return GetPrevUPoint( nullptr, &ptP) ; }
+      EGK_EXPORT bool GetPrevPoint( Point3d& ptP, bool bNotFirst = false) const
+                        { return GetPrevUPoint( nullptr, &ptP, bNotFirst) ; }
       EGK_EXPORT int  GetLineNbr( void) const
                         { return ( m_nCount > 1 ? ( m_nCount - 1) : 0) ; }
       EGK_EXPORT bool GetFirstULine( double* pdIni, Point3d* pptIni, double* pdFin, Point3d* pptFin) const ;
diff --git a/EgkSurfTriMesh.h b/EgkSurfTriMesh.h
index 163dc65..920cce9 100644
--- a/EgkSurfTriMesh.h
+++ b/EgkSurfTriMesh.h
@@ -31,10 +31,13 @@ class __declspec( novtable) ISurfTriMesh : public ISurf
       virtual int AddVertex( const Point3d& ptVert) = 0 ;
       virtual int AddTriangle( const int nIdVert[3]) = 0 ;
       virtual bool AdjustTopology( void) = 0 ;
-      virtual bool CreateByTriangulation( const PolyLine& PL) = 0 ;
+      virtual bool CreateByFlatContour( const PolyLine& PL) = 0 ;
       virtual bool CreateByExtrusion( const PolyLine& PL, const Vector3d& vtExtr) = 0 ;
+      virtual bool CreateByTwoCurves( const PolyLine& PL1, const PolyLine& PL2) = 0 ;
       virtual bool CreateByRevolution( const PolyLine& PL, const Point3d& ptAx, const Vector3d& vtAx,
                                        double dAngRot, double dStepRot) = 0 ;
+      virtual bool CreateByScrewing( const PolyLine& PL, const Point3d& ptAx, const Vector3d& vtAx,
+                                     double dAngRot, double dStepRot, double dMove) = 0 ;
       virtual int GetVertexNum( void) const = 0 ;
       virtual int GetTriangleNum( void) const = 0 ;
       virtual int GetFirstVertex( Point3d& ptP) const = 0 ;