diff --git a/EGkCurveAux.h b/EGkCurveAux.h
index dcf6b51..4efecc8 100644
--- a/EGkCurveAux.h
+++ b/EGkCurveAux.h
@@ -62,7 +62,10 @@ EGK_EXPORT ICurve* NurbsToBezierCurve( const CNurbsData& cnData) ;
 
 //----------------------------------------------------------------------------
 //! Appiattisce la curva sul suo piano medio se rientra nelle tolleranze
-EGK_EXPORT ICurve* FlattenCurve( const ICurve& crCrv, double dToler, double dAngToler) ;
+const int FLTCRV_STD = 0 ;
+const int FLTCRV_USE_EXTR = 1 ;
+const int FLTCRV_SET_EXTR = 2 ;
+EGK_EXPORT ICurve* FlattenCurve( const ICurve& crCrv, double dToler, double dAngToler, int nFlag = FLTCRV_STD) ;
 
 //----------------------------------------------------------------------------
 //! Proietta la curva sul piano indicato