Problems to get data into VisAD

Hi,

I  have some problems to get my data into VisAD.
The data are structured and splited into subdomains. Each subdomain has different values of lengthX and lengthY like the following 2D example

_______________________________________________
| | |subd. | subd. |
|subd.  |subd.  |________________|____________________|
|_____|_____|
|   subd.          |
|___________|

My first approach was to create DataReferenzImpl, FlatField and Gridded2DDoubleSet for each subdomain. With a ScalarMap(MathType, Display.RGB) it works. But now when I try to use a Display.IsoContour I get a NullPointerException.
Second I tryed to use a ProductSet with an array of Gridded2DDoubleSets.

FunctionType funcDomainTemperature = new FunctionType (domainTuple, tempType);

for(i=0; i<axis.size (); i++)
{
        double[][] pointValues = (double[][])axis.get (i);
        int[] axisLength = (int[]) dimensions.get (i);
domainSet[i] = new Gridded2DDoubleSet (domainTuple, pointValues,
        axisLength[0],
        axisLength[1]);
}

ProductSet set = new ProductSet (domainSet);
FlatField val_ff = new FlatField (funcDomainTemperature, set);

But now I get a SetException "set and type dimensions don't match" when create the FlatField. Does anyone know if there is a general problem with the Set classes or a logical mistake on my part.

Thanks
Olav