[vtkusers] can't update contourFilter unless i do contourFilter->SetValue(, )

[Liam Kurmos]

I'm trying to create an interactive tool to help me get isosurfaces
from gaussian data.

Ive created an interactorStyle and have no problem getting interaction
from the user.

>From the interactor i can change the data in my vtkImageData which was
previously set as input for the vtkContourFilter, however the changes
are not passed through to the render window.

I've called update() on the everything i can think of:
vtkImageData->Update(), vtkContourFilter->Update() the mapper etc.
but nothing seems to propagate the changes in the imageData through to
the renderWindow.

UNLESS i call contourFilter->SetValue(a,b) and change the current
isovalue in which case the contours update reflecting the changes i
immediately without needing to call update on anything.

So my question is, How can i get this effect without changing the iso value?

Liam