diff --git a/EGkSurfTriMesh.h b/EGkSurfTriMesh.h
index c1e2501..2cadb46 100644
--- a/EGkSurfTriMesh.h
+++ b/EGkSurfTriMesh.h
@@ -58,6 +58,7 @@ class __declspec( novtable) ISurfTriMesh : public ISurf
                                      double dAngRot, double dStepRot, double dMove) = 0 ;
       virtual bool DoCompacting( double dTol = EPS_SMALL) = 0 ;
       virtual bool DoSewing( const ISurfTriMesh& stmOther, const Frame3d& frOther = GLOB_FRM, double dTol = 2 * EPS_SMALL) = 0 ;
+      virtual bool IsEmpty( void) const = 0 ;
       virtual int  GetVertexCount( void) const = 0 ;
       virtual int  GetTriangleCount( void) const = 0 ;
       virtual int  GetTriangleCount( int nTFlag) const = 0 ;