Normal of the view that will display the shape being built. Must be set explicitly before adding any geometry. Must be a unit vector. This is used to validate incoming geometry - it must be orthogonal to the viewNormal. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2015 
Syntax
Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentNullException | When setting this property: A non-optional argument was NULL | 
| Autodesk.Revit.Exceptions ArgumentOutOfRangeException | When setting this property: viewNormal is not length 1.0. |