internal Curve Curve(double tol)
        {
            Curve c = AxisCurve.Curve(tol);

            if (c == null)
            {
                return(null);
            }
            IfcGrid grid = mPartOfU;

            if (grid == null)
            {
                grid = mPartOfV;
            }
            if (grid == null)
            {
                grid = mPartOfW;
            }
            if (grid != null)
            {
                c.Transform(grid.PlacementTransform());
            }
            return(c);
        }