[vtkusers] vtkPointWidget set the right position

[ChenDawnWind]

Hi everyone，I want to position a point in the model，then i use the codes like this：
	vtkSmartPointer<vtkPointWidget> pointWidget = vtkSmartPointer<vtkPointWidget>::New();	pointWidget->SetPosition(center.x, center.y, 0);	pointWidget->SetInteractor(iren);	pointWidget->On();
But the point always appear at the corner of the outline of the model.So i search the answer in the examples and google, and tried:
        vtkSmartPointer<vtkPointWidget> pointWidget = vtkSmartPointer<vtkPointWidget>::New();        pointWidget->PlaceWidget();	pointWidget->SetPosition(center.x, center.y, 0);	pointWidget->SetInteractor(iren);	pointWidget->On();
or some other codes but the problem still. So i wanna know what codes should i use to achieve my goal?Thanks!
DawnWind.ChenCSU 		 	   		  
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