Draw a line on top of a column chart

Apparently, it is not possible to have a chart with several independant horizontal axis.

What I am trying to achieve is :

• display a bar chart, organized by any category
• overlay a line (actually a single horizontal line) on top of it (to display some sort of threshold)

I tried doing the following :

[Bindable] public var columnsDataProvider : ArrayCollection = 
  new ArrayCollection([{"Category" : "Cat1", "Value" : 10},
                       {"Category" : "Cat2", "Value" : 20}]);

[Bindable] public var lineDataProvider : ArrayCollection = 
    new ArrayCollection([{"X" : 0, "Y" : 10}, 
                         {"X" : 1, "Y" : 10}]);

...

<mx:ColumnChart id="columnChart"
    showDataTips="true"
    columnWidthRatio="0.5"
    paddingTop="10"
    paddingLeft="5" paddingRight="5"
    width="100%" height="100%">


    <mx:horizontalAxis>
       <mx:CategoryAxis dataProvider="{columnsDataProvider}" categoryField="Category"/>
    </mx:horizontalAxis>

    <mx:series>

        <mx:ColumnSeries id="series1" yField="Value" xField="Carrier" dataProvider="{columnsDataProvider}">
            <mx:horizontalAxis>
                 <mx:CategoryAxis id="axis1" categoryField="Category"/>
            </mx:horizontalAxis>
        </mx:ColumnSeries>

        <mx:LineSeries id="series2" yField="Y开发者_开发问答" xField="X" dataProvider="  {lineDataProvider}">
                <mx:horizontalAxis>
                    <mx:LinearAxis id="axis2"/>
                </mx:horizontalAxis>
        </mx:LineSeries>
    </mx:series>

This is the closest to what I want, except that the line does not start span all the graphs vertically (it is drawn only between the two columns of my bar chart).

Is it possible to define a completely independant horizontal axis ?

I also tried drawing directly on the canvas, but the canvas.lineTo() method only works in "data" coordinate ; I would need something that works in "chart/canvas/absolute/whatever" coordinates.

Any help on that ?

Thanks PH

<mx:ColumnChart id="columnChart" dataProvider="{columnsDataProvider}"
showDataTips="true" columnWidthRatio="0.5"
paddingTop="10"
paddingLeft="5" paddingRight="5"
width="100%" height="100%">
<mx:horizontalAxisRenderers>
    <mx:AxisRenderer axis="{h1}" />
    <mx:AxisRenderer axis="{h2}" visible="false" />
</mx:horizontalAxisRenderers>
<mx:verticalAxis>
    <mx:LinearAxis id="v1"/>
</mx:verticalAxis>
<mx:series>
    <mx:ColumnSeries id="series1" yField="Value" xField="Category">
        <mx:horizontalAxis>
           <mx:CategoryAxis id="h1" categoryField="Category"/>
        </mx:horizontalAxis>
    </mx:ColumnSeries>
    <mx:LineSeries yField="Y" xField="X" dataProvider="{lineDataProvider}">
        <mx:horizontalAxis>
           <mx:LinearAxis id="h2" maximum="1"/>
        </mx:horizontalAxis>
    </mx:LineSeries>
</mx:series>