Direction of local Fabric Sheet Y axis in bending polyline LCS. 
   Namespace:   Autodesk.Revit.DB.Structure  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 16.0.0.0 (16.0.0.0) 
  Since:  2016 
Syntax
Remarks
 Note that bending line may be rotated before it is placed in Fabric Sheet local coordinate system. This vector allows to calculate rotation angle or Trf.