AE 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
    }

}