code: def add_text(self, coords, text, color=(0, 0, 0)):
          
          source = vtk.vtkVectorText()
          source.SetText(text)
          mapper = vtk.vtkPolyDataMapper()
          mapper.SetInputConnection(source.GetOutputPort())
          follower = vtk.vtkFollower()
          follower.SetMapper(mapper)
          follower.GetProperty().SetColor(color)
          follower.SetPosition(coords)
          follower.SetScale(0.5)
          self.ren.AddActor(follower)
          follower.SetCamera(self.ren.GetActiveCamera())
docs: Add text at a coordinate.
  
          Args:
              coords: Coordinates to add text at.
              text: Text to place.
              color: Color for text as RGB. Defaults to black.