diff --git a/EGkGeoFrame3d.h b/EGkGeoFrame3d.h
index 353958c..2e40476 100644
--- a/EGkGeoFrame3d.h
+++ b/EGkGeoFrame3d.h
@@ -20,6 +20,8 @@ class PolyLine ;
 //-----------------------------------------------------------------------------
 class __declspec( novtable) IGeoFrame3d : public IGeoObj
 {
+   public :                      // IGeoObj
+      IGeoFrame3d* Clone( void) const override = 0 ;
    public :
       virtual bool CopyFrom( const IGeoObj* pGObjSrc) = 0 ;
       virtual bool Set( const Point3d& ptOrig, const Vector3d& vtDirX, 
diff --git a/EGkGeoPoint3d.h b/EGkGeoPoint3d.h
index 2ca7067..553f0af 100644
--- a/EGkGeoPoint3d.h
+++ b/EGkGeoPoint3d.h
@@ -18,6 +18,8 @@
 //-----------------------------------------------------------------------------
 class __declspec( novtable) IGeoPoint3d : public IGeoObj
 {
+   public :                      // IGeoObj
+      IGeoPoint3d* Clone( void) const override = 0 ;
    public :
       virtual bool CopyFrom( const IGeoObj* pGObjSrc) = 0 ;
       virtual bool Set( const Point3d& ptP) = 0 ;
diff --git a/EGkGeoVector3d.h b/EGkGeoVector3d.h
index 2805422..fb7e54c 100644
--- a/EGkGeoVector3d.h
+++ b/EGkGeoVector3d.h
@@ -20,6 +20,8 @@ class PolyLine ;
 //-----------------------------------------------------------------------------
 class __declspec( novtable) IGeoVector3d : public IGeoObj
 {
+   public :                      // IGeoObj
+      IGeoVector3d* Clone( void) const override = 0 ;
    public :
       virtual bool CopyFrom( const IGeoObj* pGObjSrc) = 0 ;
       virtual bool Set( const Vector3d& vtV) = 0 ;
diff --git a/EGkVolZmap.h b/EGkVolZmap.h
index 7a479cd..0a442fa 100644
--- a/EGkVolZmap.h
+++ b/EGkVolZmap.h
@@ -47,6 +47,8 @@ typedef std::vector<IntLineZmapInfo>    ILZIVECTOR ;
 //----------------------------------------------------------------------------
 class __declspec( novtable) IVolZmap : public IGeoObj
 {
+   public :                      // IGeoObj
+      IVolZmap* Clone( void) const override = 0 ;
    public :
       virtual bool CopyFrom( const IGeoObj* pGObjSrc) = 0 ;
       virtual bool Clear( void) = 0 ;