[vtkusers] Rotation of a volume

[Rhys Thomas]

I am currently attempting to rotate and translate a volume stored as 
vtkStructuredPoints using vtkVolume::PokeMatrix (I am using VC++ 6). The 
matrix is a vtkMatrix4x4 that takes data from elsewhere in the program. 
This arrangement worked well until I tried to add another prop to the 
pipeline, a vtkActor containing a vtkSphereSource. The trouble that I am 
now experiencing is that the volume is now not appearing in the centre 
of the window, and seems to be rotating not about the centre of the 
volume, but approximately about the bottom right corner. My pipeline is 
set up as follows:

vtkRenderWindow<-vtkRenderer<-vtkVolume<-vtkVolumeMapper<-vtkStructuredPoints
                             |
                             vtkActor<-vtkPolyMapper<-vtkSphereSource

I have not fully implemented the transformation for the sphere, however 
it too appears off centre in the window, and by a different amount to 
the volume. The sphere is much smaller than the volume being displayed 
(it has a radius of 1, compared to the volume of size 512x512x246, 
although this may change). The volume and the sphere will eventually be 
transformed by different transformations, and the sphere will probably 
be replaced with another shape, the position of which will have to be 
known relative to the co-ordinates of the volume.

Is there anything that can be done to rectify this situation? I have 
attempted to set origins and set a camera position without success.

Thanks

Rhys Thomas

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