The dimension origin. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 16.0.0.0 (16.0.0.0) 
  Since:  2015 Subscription Update 
Syntax
Remarks
 The origin is the middle point of the dimension line that makes up the dimension. This property is for use with single-segment dimensions only. For multi-segment dimensions use the corresponding property of the DimensionSegment class.