Grpahs: Dual Axis Charts

[kaeserea]

Hello!

I'd like to display a vertical polar clusteres bars chart (graph type=21) which should look like this:
[tt]
^ ^
| | |
| | | | |
| || ||| |
| |||| |||| |
|--------------------------|
| |
| | | | |
| | || | | |
| |||| |||| |
|--------------------------|
[/tt]

normally you can only say
setAxisAssignment(getSeries(x),1);
(put a series down on the lower axis)

but
setAxisAssignment(getGroups(1),1);
would be what I want, but it doesn't work.

So I'd like to put whole groups (not series) down on the lower Axis. Does anybody know how to do this?

Thanx a lot
Eva