docstr: Return the transform mapping this item's local coordinate system to the 
  view coordinate system.
code: def viewTransform(self):
      """Return the transform mapping this item's local coordinate system to the
      view coordinate system."""
      tr = self.__transform
      p = self
      while True:
          p = p.parentItem()
          if p is None:
              break
          tr = p.transform() * tr
      return Transform3D(tr)
  
imports: from OpenGL.GL import *
  from OpenGL import GL
  from ..None import Transform3D
  from ..Qt import QtCore
label_desc: Use image node_id 15 for calling the GLGraphicsItem obj's underlying member method code with example usage: obj.viewTransform() and returns: Transform3D