Mapping sensor coordinates to display

Question

I have an EM sensor which gives me position and orientation. I can display these values on screen. What i want to do is map just the x and y position coordinates onto a 2d dicom image using VTK so that when i move the sensor i can track its position on the image.

The image is a 512 x 512 dicom image with 0.45 spacing.

i am visualizing the sensor position on the image using a vtk sphere. Right now the positions are not displayed properly on the image.

double image_coord[2];
//pPno[0] and pPno[1] are the x and y coordinates of the sensor
image_coord[0] = pPno[0] + 115.2; //translating to the center of the 512x512 image with 0.45 spacing
image_coord[1] = pPno[1] + 115.2;


vtkSmartPointer<vtkCoordinate> coordinate = vtkSmartPointer<vtkCoordinate>::New();
coordinate->SetCoordinateSystemToViewport();
coordinate->SetValue(image_coord[0], image_coord[1], 0);
coordinate->GetComputedViewPortValue(imageViewer->GetRenderer());


sphere->SetCenter(100, 100, 0);
sphere->SetRadius(6);
    
        
mapper->SetInputConnection(sphere->GetOutputPort());
actor1->SetMapper(mapper);
actor1->GetProperty()->SetColor(1, 1, 0);
        
imageViewer->GetRenderer()->AddActor(actor1);
actor1->SetPosition(image_coord[0], image_coord[1],0);

imageViewer->Render();

inter->ProcessEvents();