Envelope 转为Polygon

                        IEnvelopePtr ipEnv ;

                        hr = m_ipMapCtrl ->TrackRectangle(& ipEnv);

                         IPointPtr ipPointUL ;

                         IPointPtr ipPointUR ;

                         IPointPtr ipPointLL ;

                         IPointPtr ipPointLR ;

                         ipEnv->get_UpperLeft (&ipPointUL);

                         ipEnv->get_UpperRight (&ipPointUR);

                         ipEnv->get_LowerLeft (&ipPointLL);

                         ipEnv->get_LowerRight (&ipPointLR);

                         IPointCollectionPtr ipPointCollection (CLSID_Polygon);

                         ipPointCollection->AddPoint (ipPointUL);

                         ipPointCollection->AddPoint (ipPointLL);

                         ipPointCollection->AddPoint (ipPointLR);

                         ipPointCollection->AddPoint (ipPointUR);

                         ipGeo=ipPointCollection ;