Gets the length of this vector. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
Remarks
 In 3-D Euclidean space, the length of the vector is the square root of the sum of the three coordinates squared.