diff --git a/EGkVolZmap.h b/EGkVolZmap.h
index b158195..e7d5f5e 100644
--- a/EGkVolZmap.h
+++ b/EGkVolZmap.h
@@ -32,7 +32,7 @@ class __declspec( novtable) IVolZmap : public IGeoObj
       virtual bool Create( const Point3d& ptO, double dDimX, double dDimY, double dDimZ, double dStep, bool bTriDex) = 0 ;
       virtual bool CreateEmpty( const Point3d& ptO, double dDimX, double dDimY, double dDimZ, double dStep, bool bTriDex) = 0 ;
       virtual bool CreateFromFlatRegion( const ISurfFlatRegion& Surf, double dDimZ, double dStep, bool bTriDex) = 0 ;
-      virtual bool CreateFromTriMesh( const ISurfTriMesh& Surf, double dStep, bool bTriDex, double dExtraBox = 0.) = 0 ;
+      virtual bool CreateFromTriMesh( const ISurfTriMesh& Surf, double dStep, bool bTriDex, double dExtraBox = 100 * EPS_SMALL) = 0 ;
       virtual int  GetBlockCount( void) const = 0 ;
       virtual int  GetBlockUpdatingCounter( int nBlock) const = 0 ;
       virtual bool GetBlockTriangles( int nBlock, TRIA3DEXVECTOR& vTria) const = 0 ;