Tells if the spline is rational or not. If it is true (rational), then the NURBS is a piecewise rational polynomial function. If it is false (non-rational), then the NURBS is a piecewise polynomial function. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 17.0.0.0 (17.0.1090.0) 
  Since:  2016