[vtkusers] transform vtk dataset coordinate to global

[Michael Thomas]

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Hi Guys,

I would like to know how its possible to transform in VTK a dataset coordinate to global corrdinate. 
For ex: I have a 3D Model which has been enabled to be picked. Everytime its picked I put a marker on the model & I store the cellId of the picked cell. I am required to animate the 3D Model & the marker needs to move with the model.

What I tried to do when I change the model position for each animation frame is to get the vtkCell using the stored cellId. From there I try to retrieve the cell position for any one of the 3 cell points

>> cell->GetPoints()->GetPoint( 0, pos);

The position retrieved seems to be in dataset coordinates ( Is this correct ???)

Instead of the above, I also tried to retrieve the Global position of the vtkCell object using 

>> cell->EvaluateLocation( subId, pcoords, gcoords, weights). 

But the "gcoords[]" returned seem to have similar values like GetPoint() showed above and don't seem to be in global coordinates.

I tried using vtkCoordinate class but they seem to do the transformation between viewport & global coordinates and don't seem to have dataset coordinate transformation. vtkRenderer class also have transformations between Display(viewport) & world(Global) coordinates.

The Visualisation Toolkit book has some info wrt to coordinates in Chapter 8, section 3( i.e 8.3 ). I am wondering if anyone has implemented any class that encapsulates that logic( I expected vtkCoordinate to do this but alas!)

So I am caught out hopelessly after breaking my head over several techniques & I would be grateful if someone can provide me with that crucial tip that will open my mind to the vast possibilities in vtk coordinate space :).

Thank You.

Cheers,
Michael Thomas