[vtkusers] Problem between vtkActors coordinates and World view coordinates

[mathieu.biston at irisa.fr]

Hello,

I've got a problem with coordinate system in a render scene : each 
vtkActor behaves using its own coordinate system.

In my application, users can load surfaces and then put landmarks on 
them. Using a vtkPointPicker on the surface, a vtkSphere is created with 
the given coordinates and added to the scene as a vtkActor.

I want the user to be able to drag a landmark over the surface. When 
using the coordinates provided by the vtkPointPicker to select a new 
location, the setPosition method fails to relocate the vtkActor at the 
expected location.
It seems that each vtkActor of the scene has its own coordinate system.

I solved this problem using tricky conversions but I was wondering if 
there is a more appropriate solution, for instance if there is any 
method to put all vtkActors of a scene in the same coordinate system.

Thanks in advance

Mathieu