ModelDoc2 ModelDoc2 = default(ModelDoc2);

            ModelDoc2 = (ModelDoc2)iSwApp.ActiveDoc;

            int DocType = 0;

            DocType = ModelDoc2.GetType();

            if (DocType != (int)swDocumentTypes_e.swDocASSEMBLY)

            {

                Debug.Print("An assembly document is not active");

                return;

            }

            ModelDoc2.ClearSelection2(true);

            AssemblyDoc AssemblyDoc = default(AssemblyDoc);

            AssemblyDoc = (AssemblyDoc)ModelDoc2;

            AssemblyDoc .XXXXXXXXXXXXXXXXX

             QUE：what funtion using , I can get the assembly's gravity coordinates?

             Thanks a lot！