How to get a near/far plane in parallel mode ?(C++)

I want to get those planes for knowing what I can see.
Those planes is defined below.

Use ON_Viewport::GetNearPlane and ON_Viewport::GetFarPlane.

CRhinoView* view = RhinoApp().ActiveView();
if (view)
{
  const ON_Viewport& vp = view->ActiveViewport().VP();
  ON_Plane near_plane, far_plane;
  if (vp.GetNearPlane(near_plane))
  {
    // TODO...
  }
}

Thanks a lot !