vtk BoxWidget coordinates

Hello!
I define boxWidget->PlaceWidget(xmin, xmax, ymin, ymax, zmin, zmax).
Than, When I try to “read” again the same coordinates, the values are completely different and I can’t understand why…? I am sending here part of the code about this issue (0.085 is the pixel size). Could someone please help me?

(…)

vtkBoxWidget boxWidget = vtkBoxWidget::New();*
** boxWidget->SetInteractor(rendWindInt);**
** boxWidget->SetProp3D(volume1);**
** boxWidget->PlaceWidget(0, 857 * 0.085, 0, 883 * 0.085, 0, 32);**
** boxWidget->SetPlaceFactor(1);**

** renderWindow->SetSize(1000, 600);**
** rendWindInt->Initialize();**
** boxWidget->On();**
** rendWindInt->Start();**

vtkSmartPointer pd = vtkSmartPointer::New();
** boxWidget->GetPolyData(pd);**
** double* bound = pd->GetBounds(); **

** double boundXmin = floor(bound[0] / x_voxelsize);**
** double boundXmax = floor(bound[1] / x_voxelsize);**
** double boundYmin = floor(bound[2] / y_voxelsize);**
** double boundYmax = floor(bound[3] / y_voxelsize);**
** double boundZmin = floor(bound[4] / z_voxelsize);**
** double boundZmax = floor(bound[5] / z_voxelsize);**

(…)

I was expecting that boundXmin = 0, boundXmax = 857 * 0.085, boundYmin = 0, boundYmax = 883 * 0.085, boundZmin = 0, boundZmax = 32.
But instead, I obtained:
boundXmin = 214, boundXmax = 642
boundYmin = 220, boundYmax = 662
boundZmin = 8, boundZmax = 24

Any help??