title: How to rotate a vtkVectorText to face a direction?
body: <p>I would like to have a text at a certain position ([1,1,1] in the below example), which face the direction from the origin [0,0,0] to the position the text is [1,1,1]</p>
  
  <p>I've tried to compute two rotation angles between xy and xz axis and applied them with the RotateWXYZ transformation but it doesn't work.
  The function GetAngleBetweenPoints compute the angle between three coordinates in this case </p>
  
  <p>In addition I would like the text to be centered if possible.</p>
  
  <p>So far I have this code :</p>
  
  <pre><code>from vtk import*
  import numpy as np
  
  
  def GetAngleBetweenPoints( endPt1, connectingPt, endPt2):
      x1 = endPt1[0] - connectingPt[0]
      y1 = endPt1[1] - connectingPt[1]
      x2 = endPt2[0] - connectingPt[0]
      y2 = endPt2[1] - connectingPt[1]
      angle = np.arctan2(y1, x1) - np.arctan2(y2, x2)
      angle = angle * 360 / (2 * np.pi)
      if (angle &lt; 0) :
          angle += 360
      return angle
  
  
  textSource = vtkVectorText()
  textSource.SetText("Hello")
  textSource.Update()
  
  transfo = vtk.vtkTransform()
  transfo.Identity()
  transfo.PostMultiply()
  
  x = 1
  xo = 0
  y = 1
  yo = 0
  z =1
  zo = 1 
  #angle Z
  teta = GetAngleBetweenPoints( [x,y], [0,0], [xo,yo])
  print(teta)
  transfo.RotateWXYZ(+(teta),0, 0, 1)
  # angle Y
  teta = GetAngleBetweenPoints( [x,z], [0,0], [xo,zo])
  print(teta)
  transfo.RotateWXYZ(+(teta), 0, 1, 0)
  transfo.Translate(x,y,z)
  
  filter = vtk.vtkTransformPolyDataFilter()
  filter.SetInputConnection(textSource.GetOutputPort())
  filter.SetTransform(transfo)
  filter.Update()
  
  
  
  #Create a mapper and actor
  mapper = vtkPolyDataMapper()
  mapper.SetInputConnection(filter.GetOutputPort())
  
  actor =vtkActor()
  actor.SetMapper(mapper)
  actor.GetProperty().SetColor(1.0, 0.0, 0.0)
  
  #Create a renderer, render window, and interactor
  renderer = vtkRenderer()
  renderWindow = vtkRenderWindow()
  renderWindow.AddRenderer(renderer)
  renderWindowInteractor = vtkRenderWindowInteractor()
  renderWindowInteractor.SetRenderWindow(renderWindow)
  
  renderer.AddActor(actor)
  renderer.AddActor(vtk.vtkAxesActor())
  renderer.SetBackground(0.4, 0.3, 0.2)
  
  renderWindow.Render()
  style = vtk.vtkInteractorStyleMultiTouchCamera()
  renderWindowInteractor.SetInteractorStyle(style)
  renderWindowInteractor.Start() 
  </code></pre>