public void ComputeExtents(IEnumerable <ClassDefinition> classes)
 {
     using (FdoFeatureService service = _conn.CreateFeatureService())
     {
         IEnvelope env = service.ComputeEnvelope(classes);
         if (env != null)
         {
             _view.LowerLeftX  = env.MinX.ToString();
             _view.LowerLeftY  = env.MinY.ToString();
             _view.UpperRightX = env.MaxX.ToString();
             _view.UpperRightY = env.MaxY.ToString();
         }
     }
 }