public void drawDomainMarker(Graphics2D g2,
                                 ContourPlot plot,
                                 ValueAxis domainAxis,
                                 Marker marker,
                                 Rectangle2D dataArea) {

        if (marker instanceof ValueMarker) {
            ValueMarker vm = (ValueMarker) marker;
            double value = vm.getValue();
            Range range = domainAxis.getRange();
            if (!range.contains(value)) {
                return;
            }
  
            double x = domainAxis.valueToJava2D(value, dataArea, 
                    RectangleEdge.BOTTOM);
            Line2D line = new Line2D.Double(x, dataArea.getMinY(), x, 
                    dataArea.getMaxY());
            Paint paint = marker.getOutlinePaint();
            Stroke stroke = marker.getOutlineStroke();
            g2.setPaint(paint != null ? paint : Plot.DEFAULT_OUTLINE_PAINT);
            g2.setStroke(stroke != null ? stroke : Plot.DEFAULT_OUTLINE_STROKE);
            g2.draw(line);