[vtkusers] ... An strange rendering?

[jsl n]

Hi friends,

  I've just the following problem when rendering a .OBJ mesh. The first attached
screenshot is obtained with the following setup for the VTK's camera:

camera->SetFocalPoint(0, 0, 0);
camera->SetPosition(0, 0, 5.1);
camera->ComputeViewPlaneNormal();
camera->SetViewUp(0, 1, 0);
camera->SetViewAngle(22.2);

It looks right...

The point is that changing the SetPosition() method as following:

camera->SetFocalPoint(0, 0, 0);
camera->SetPosition(0, 0, -5.1);  // Here is the only change.
camera->ComputeViewPlaneNormal();
camera->SetViewUp(0, 1, 0);
camera->SetViewAngle(22.2);

rendering becomes messed up (backfaces and bad z-fighting), as depicted in the
second attached screenshot. Why placing the camera position in the Z-negative
gets wrong results?

I'd be so grateful with you for any advice.
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