diff --git a/EGkSurfTriMesh.h b/EGkSurfTriMesh.h
index 4e65b08..7c51585 100644
--- a/EGkSurfTriMesh.h
+++ b/EGkSurfTriMesh.h
@@ -88,8 +88,8 @@ class __declspec( novtable) ISurfTriMesh : public ISurf
       virtual bool GetTriangleSmoothNormals( int nId, TriNormals3d& TNrms) const = 0 ;
       virtual ISurfTriMesh* CloneTriangle( int nTria) const = 0 ;
       virtual bool GetLoops( POLYLINEVECTOR& vPL) const = 0 ;
-      virtual bool GetSilhouette( const Vector3d& vtDir, double dTol, POLYLINEVECTOR& vPL, bool bAllTria = false) const = 0 ;
-      virtual bool GetSilhouette( const Plane3d& plPlane, double dTol, POLYLINEVECTOR& vPL, bool bAllTria = false) const = 0 ;
+      virtual bool GetSilhouette( const Vector3d& vtDir, double dTol, POLYLINEVECTOR& vPL, bool bAllTria = false, double dLinTol = 100. * EPS_SMALL) const = 0 ;
+      virtual bool GetSilhouette( const Plane3d& plPlane, double dTol, POLYLINEVECTOR& vPL, bool bAllTria = false, double dLinTol = 100. * EPS_SMALL) const = 0 ;
       virtual int  GetFacetCount( void) const = 0 ;
       virtual int  GetFacetSize( void) const = 0 ;
       virtual int  GetFacetFromTria( int nT) const = 0 ;