[vtkusers] Help with vtkWindowToImageFilter

[Michael Györffy]

Hello:
	I'm a new user and am trying to save images from generated
PolyData.
Through the excellent help I've received from this forum (Thank you) I'm
trying to take the screenshot and convert it to ImageData using
vtkWindowToImageFilter.
	 I get an error of:"no matching function for call
to
`vtkRenderWindow::GetOutput ()'".
	I don't understand why this doesn't work, but works in examples
such as OffScreenCone.tcl.

	Briefly, the layout of my program is:
		PolyDataReader
		PolyDataMapper
		Actor
		Renderer
		Renderwindow
then I use the following:
	vtkWindowToImageFilter *w2if = vtkWindowToImageFilter::New();
  		w2if->SetInput(renWin->GetOutput());

	vtkPNMWriter *pnmwriter=vtkPNMWriter::New();
  		pnmwriter->SetInput(w2if->GetOutput());
		pnmwriter->SetFileName("3Dimagedata.pnm");
  		pnmwriter->Write();
	Any suggestions would be very much appreciated.
Thanks,

Mike