ax = new double[3];
    public void calculateExtrusion() {        ax = new double[3];        if ((Math.abs(n.getX()) < v) && (Math.abs(n.getY()) < v)) {            x = MathUtils.crossProduct(DXFConstants.DEFAULT_Y_AXIS_VECTOR, n);        } else {            x = MathUtils.crossProduct(DXFConstants.DEFAULT_Z_AXIS_VECTOR, n);        }        y = MathUtils.crossProduct(x, n);    }