[vtkusers] GetBounds() for custom Reader class returning vtkUnstructuredGrid*

[Marc Niethammer]

I implemented a new reader class for a custom format that returns a
vtkUnstructuredGrid*. It is used as the input for an
instance of vtkDataSetMapper. Everything works fine as long as my data
lies within the bounds (-1,1,-1,1,-1,1). If this is not the case nothing
is displayed (or at least it is not visible). 

I believe that this is a problem with the GetBounds() method. I think
(correct me if I'm wrong) that on an update the actor calls the
GetBounds() function on the input of its associated mapper function. It
should thus call the GetBounds() function of the vtkUnstructuredGrid (as
given by vtkDataSet) and the extent should be automatically determined.

Do I have to set the extent of my data somewhere explicitly instead? Or do
I have to overload a certain method in my reader class?

-- Marc