ArcGIS Engine开发系列：将地图导出为图片的两种方法

??? 在ArcGIS的开发中，我们经常需要将当前地图打印（或是转出）到图片文件中。将Map或Layout中的图象转出有两种方法，一种为通过
IActiveView的OutPut函数，另外一种是通过IExport接口来实现。第一种方法导出速度较快，实现也比较方便，但该方法对于图片的行或
列数超过10000左右时，导出经常会失败（具体原因未知），第二种方法导出速度较慢，但效果较好，且可以在导出过程中通过ITrackCancel来中
止导出操作。
????? 通过IActiveView的方式导出是通过创建Graphics对象来实现，具体示例代码如下：

/// <summary>/// 将Map上指定范围（该范围为规则区域）内的内容输出到Image,注意，当图片的行数或列数超过10000左右时，出现原因示知的失败/// </summary>/// <param name="pMap">需转出的MAP</param>/// <param name="outRect">输出的图片大小</param>/// <param name="pEnvelope">指定的输出范围（为Envelope类型）</param>/// <returns>输出的Image 具体需要保存为什么格式，可通过Image对象来实现</returns>public static Image SaveCurrentToImage(IMap pMap, Size outRect, IEnvelope pEnvelope) { //赋值 tagRECT rect = new tagRECT(); rect.left = rect.top = 0; rect.right = outRect.Width; rect.bottom = outRect.Height; try { //转换成activeView，若为ILayout，则将Layout转换为IActiveView IActiveView pActiveView = (IActiveView)pMap; // 创建图像,为24位色 Image image = new Bitmap(outRect.Width, outRect.Height); //, System.Drawing.Imaging.PixelFormat.Format24bppRgb); System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image); // 填充背景色(白色) g.FillRectangle(Brushes.White, 0, 0, outRect.Width, outRect.Height); int dpi = (int)(outRect.Width / pEnvelope.Width); pActiveView.Output(g.GetHdc().ToInt32(), dpi, ref rect, pEnvelope, null); g.ReleaseHdc(); return image; } catch (Exception excp) { MessageBox.Show(excp.Message + "将当前地图转出出错，原因未知", "出错提示", MessageBoxButtons.OK, MessageBoxIcon.Error); return null; } }


?? 通过IExport接口实现的导出，也需要通过IActiveView的OutPut来实现，但其转出句柄为IExport的StartExporting函数返回的DC,具体示例代码如下：

//输出当前地图至指定的文件???? ??public?void?ExportMapExtent(IActiveView?pView,?Size?outRect,string?outPath) ??{??????????? ??????try??????{ ??????????//参数检查 ??????????if?pView?==?null?) ??????????{ ??????????????throw?new?Exception("输入参数错误,无法生成图片文件!"); ??????????}?? ??????????//根据给定的文件扩展名，来决定生成不同类型的对象 ??????????ESRI.ArcGIS.Output.IExport?export?=?null; ??????????if?(outPath.EndsWith(".jpg")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportJPEGClass(); ??????????} ??????????else?if?(outPath.EndsWith(".tiff")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportTIFFClass(); ??????????} ??????????else?if?(outPath.EndsWith(".bmp")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportBMPClass(); ??????????} ??????????else?if?(outPath.EndsWith(".emf")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportEMFClass(); ??????????} ??????????else?if?(outPath.EndsWith(".png")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportPNGClass(); ??????????} ??????????else?if?(outPath.EndsWith(".gif")) ??????????{ ??????????????export?=?new?ESRI.ArcGIS.Output.ExportGIFClass(); ??????????} ????????????export.ExportFileName?=?outPath; ??????????IEnvelope?pEnvelope?=?pView.Extent; ??????????//导出参数??????????? ??????????export.Resolution?=?300; ??????????tagRECT?exportRect?=?new?tagRECT(); ??????????exportRect.left?=?exportRect.top?=?0; ??????????exportRect.right?=?outRect.Width; ??????????exportRect.bottom?=?(int)(exportRect.right?*?pEnvelope.Height?/?pEnvelope.Width); ??????????ESRI.ArcGIS.Geometry.IEnvelope?envelope?=?new?ESRI.ArcGIS.Geometry.EnvelopeClass(); ??????????//输出范围 ??????????envelope.PutCoords(exportRect.left,?exportRect.top,?exportRect.right,?exportRect.bottom); ??????????export.PixelBounds?=?envelope; ??????????//可用于取消操作 ??????????ITrackCancel?pCancel?=?new?CancelTrackerClass(); ??????????export.TrackCancel?=?pCancel; ??????????pCancel.Reset(); ??????????//点击ESC键时，中止转出 ??????????pCancel.CancelOnKeyPress?=?true; ??????????pCancel.CancelOnClick?=?false; ??????????pCancel.ProcessMessages?=?true; ??????????//获取handle ??????????System.Int32?hDC?=?export.StartExporting(); ??????????//开始转出 ??????????pView.Output(hDC,?(System.Int16)export.Resolution,?ref?exportRect,?pEnvelope,?pCancel); ??????????bool?bContinue?=?pCancel.Continue(); ??????????//捕获是否继续 ??????????if?(bContinue) ??????????{?????????????????????????????? ??????????????export.FinishExporting(); ??????????????export.Cleanup(); ??????????} ??????????else??????????{?????????????????? ??????????????export.Cleanup(); ??????????} ??????????bContinue?=?pCancel.Continue();??????????????? ??????} ??????catch?(Exception?excep) ??????{ ??????????//错误信息提示 ??????} ??}?