GlobeControl如何实现鼠标滚轮缩放？

private void MainForm_Load(object sender, EventArgs e)

        {



 //向Arcglobe中添加鼠标滚轮放大缩小功能09.4.20刘现印添加

            this.MouseWheel += new System.Windows.Forms.MouseEventHandler(axGlobeControl1_OnMouseWheel);

        }

        private void axGlobeControl1_OnMouseWheel(object sender, MouseEventArgs e)

        {

            try

            {

                Cursor.Current = new System.Windows.Forms.Cursor(@..\..\Resources\ZOOMINOUT.CUR);//将鼠标样式变换为自定义的鼠标样式

                //m_cursor = new System.Windows.Forms.Cursor(@..\..\Resources\ZOOMINOUT.CUR);

                System.Drawing.Point pSceLoc = axGlobeControl1.PointToScreen(axGlobeControl1.Location);

                System.Drawing.Point Pt = this.PointToScreen(e.Location);

                if (Pt.X < pSceLoc.X || Pt.X > pSceLoc.X + axGlobeControl1.Width || Pt.Y < pSceLoc.Y || Pt.Y > pSceLoc.Y + axGlobeControl1.Height)

                {

                    return;

                }



                double scale = 0.2;                           

                if (e.Delta < 0) scale = -scale;



                IGlobeCamera pGlobeCamera = axGlobeControl1.GlobeCamera;

                ICamera pCamera = pGlobeCamera as ICamera;

                IGlobeDisplay pGlobeDisplay = axGlobeControl1.GlobeDisplay;

                if (pGlobeCamera.OrientationMode == esriGlobeCameraOrientationMode.esriGlobeCameraOrientationGlobal)

                {

                    double zt, xo, yo, zo;

                    pGlobeCamera.GetObserverLatLonAlt(out xo, out yo, out zo);

                    pGlobeDisplay.GetSurfaceElevation(xo, yo, true, out zt);

                    IPoint pObserver = new PointClass();

                    pObserver.PutCoords(xo, yo);

                    double zt1 = zt * (UnitSacleToMeter(axGlobeControl1.Globe.GlobeUnits));

                    zo = (zo - zt1) * (1 + scale);

                    pGlobeCamera.SetObserverLatLonAlt(xo, yo, zo);

                }

                else

                {

                    pCamera.ViewingDistance += pCamera.ViewingDistance * scale;

                }

                axGlobeControl1.GlobeDisplay.RefreshViewers();            

            }

            catch

            {

            }

        }



  /// <summary>

        /// 其中UnitSacleToMeter方法为获取单位转换为米的系数

        /// </summary>

        /// <param name=unit></param>

        /// <returns></returns>

        public static double UnitSacleToMeter(esriUnits unit)

        {

            switch (unit)

            {

                case esriUnits.esriKilometers:

                    return 1000;

                case esriUnits.esriMeters:

                    return 1;

                default:

                    return -1;

            }

        }