Engine中旋转地图后如何指定范围输出为图片？

//rotation为地图旋转角度（单位为角度）

​private void Do_Export(object sender, EventArgs e)

        {

            IMap map = axMapControl1.Map;

            IActiveView actView = axMapControl1.ActiveView;

            IGraphicsContainer GC = map.BasicGraphicsLayer as IGraphicsContainer;

            IEnumElement enumElement = GC.LocateElementsByEnvelope(axMapControl1.ActiveView.Extent);

            enumElement.Reset();

            IElement element = enumElement.Next();

            geo = element.Geometry;



            //旋转输出范围几何

            ITransform2D trans2D = geo as ITransform2D;

            trans2D.Rotate(((IArea)geo).Centroid, rotation*Math.PI/180); 

            IEnvelope aftRot = geo.Envelope as IEnvelope;



            ExportImage(m_mapControl.ActiveView, crtPath + \\output.jpg, aftRot, (int)aftRot.Width, (int)aftRot.Height);

        }



        public static void ExportImage(IActiveView pActiveView, string sFilePath, IEnvelope outputExtent, int width, int height)

        {

            IExport pExporter = new ExportJPEGClass();

            IEnvelope pEnvelope = new EnvelopeClass();



            int pResolution = width * (int)(pActiveView.ScreenDisplay.DisplayTransformation.Resolution) / pActiveView.ExportFrame.right;



            tagRECT ptagRECT;

            ptagRECT.left = 0;

            ptagRECT.top = 0;

            ptagRECT.right = width;

            ptagRECT.bottom = height;



            pEnvelope.PutCoords(ptagRECT.left, ptagRECT.bottom, ptagRECT.right, ptagRECT.top);

            pExporter.Resolution = pResolution;

            pExporter.ExportFileName = sFilePath;

            pExporter.PixelBounds = pEnvelope;



            //指定输出范围

            pActiveView.Output(pExporter.StartExporting(), (System.Int16)pExporter.Resolution, ref ptagRECT, outputExtent, null);



            pExporter.FinishExporting();

            pExporter.Cleanup();

        }