C# & GDAL 学习二

一 引言

在C# & GDAL 学习一中我写了如何用GDAL读取栅格图像的基本信息。

本篇内容是接着学习一，如何保存一个栅格图像。

在这里不加啰嗦了，主要代码我会把注释写的很清楚。

二 代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using OSGeo.GDAL;
using System.Drawing;
using System.Drawing.Imaging;
namespace GDALRead
{
    class Program
    {
        public static void usage()
        {
            Console.WriteLine("usage");
            System.Environment.Exit(-1);
        }
     public  static void Main(string[] args)
        {
       
         if (args.Length < 2) usage();

         Console.WriteLine("args包括两个字符串，一个是filename及路径，一个是outfilename及路径"); 

         try
         {
             Gdal.AllRegister();
             Dataset ds = Gdal.Open(args[0],Access.GA_ReadOnly);//读取filename栅格图像
             if (ds==null)
             {
                Console.WriteLine("Can't open " + args[0]); 
                 System.Environment.Exit(-1); 
             }
             Console.WriteLine("raster dataset parameters:");
             Console.WriteLine("  Projection:" + ds.GetProjectionRef());
             Console.WriteLine("  Rastercount:" + ds.RasterCount);//RasterCount是波段数
             Console.WriteLine("  RasterSize (" + ds.RasterXSize + "," + ds.RasterYSize + ")");

             /************************************************************************/
             /* Get Driver                                                                     */
             /************************************************************************/
             Driver drv = ds.GetDriver();
             if (drv ==null)
             {
                 Console.WriteLine("Can't get driver");
                 System.Environment.Exit(-1);
             }
             Console.WriteLine("using driver" + drv.LongName);
             /************************************************************************/
             /* Get raster band                                                                    */
             /************************************************************************/
             for (int iBand=1;iBand<=ds.RasterCount;iBand++)
             {
                 Band band = ds.GetRasterBand(iBand);
                 Console.WriteLine("Band" + iBand + ":");
                 Console.WriteLine("   DataType:" + band.DataType);
                 Console.WriteLine("   Size (" + band.XSize + "," + band.YSize + ")");
                 Console.WriteLine("   PaletteInterp: " + band.GetRasterColorInterpretation().ToString()); //调色板图像

              
             }
             /************************************************************************/
             /* Processing the raster    
             /************************************************************************/
             SaveBitmapBuffered(ds, args[1]);
         }
             
         catch (System.Exception ex)
         {
             Console.WriteLine("Application error: " + ex.Message);
         }
         Console.ReadLine();
        }
        private static void SaveBitmapBuffered(Dataset ds, string filename) 
        {
            Band redBand = ds.GetRasterBand(1);
  
            if (redBand.GetRasterColorInterpretation() != ColorInterp.GCI_RedBand) 
                
            { 
                 Console.WriteLine("Non RGB images are not supported by this sample! ColorInterp = " +  
                 redBand.GetRasterColorInterpretation().ToString()); 
                         return; 
            } 
  
            if (ds.RasterCount < 3)  
            { 
                         Console.WriteLine("The number of the raster bands is not enough to run this sample"); 
                         System.Environment.Exit(-1); 
             }

             Band greenBand = ds.GetRasterBand(2);

             if (greenBand.GetRasterColorInterpretation() != ColorInterp.GCI_GreenBand) 
             { 
                     Console.WriteLine("Non RGB images are not supported by this sample! ColorInterp = " +  
                     greenBand.GetRasterColorInterpretation().ToString()); 
                         return; 
             } 
  
             Band blueBand = ds.GetRasterBand(3); 
          
             if (blueBand.GetRasterColorInterpretation() != ColorInterp.GCI_BlueBand) 
             { 
                 Console.WriteLine("Non RGB images are not supported by this sample! ColorInterp = " +  
                 blueBand.GetRasterColorInterpretation().ToString()); 
                         return; 
                 } 
  
         int width = redBand.XSize; 
         int height = redBand.YSize; 
  
         // Create a Bitmap to store the GDAL image in 
         Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format32bppRgb); 
 
        DateTime start = DateTime.Now; 
          
         byte[] r = new byte[width * height]; 
         byte[] g = new byte[width * height]; 
         byte[] b = new byte[width * height]; 
  
         redBand.ReadRaster(0, 0, width, height, r, width, height, 0, 0); 
         greenBand.ReadRaster(0, 0, width, height, g, width, height, 0, 0); 
         blueBand.ReadRaster(0, 0, width, height, b, width, height, 0, 0); 
         TimeSpan renderTime = DateTime.Now - start;//计算生成一幅新的栅格图像所需要的时间
         Console.WriteLine("SaveBitmapBuffered fetch time: " + renderTime.TotalMilliseconds + " ms"); 
  
         int i, j; 
         for (i = 0; i< width; i++)  
         { 
             for (j=0; j<height; j++) 
             { 
                 Color newColor = Color.FromArgb(Convert.ToInt32(r[i+j*width]),Convert.ToInt32(g[i+j*width]), Convert.ToInt32(b[i+j*width])); 
                 bitmap.SetPixel(i, j, newColor); 
             } 
         } 
 
        bitmap.Save(filename); 
 
        } 
       
    }
   
}

三 运行结果

我用QQ截了一个RGB的图像（22k），程序运行的结果如图：

另外，在我的GDALRead\bin\Debug目录下新生成了一个一样的，但是.tif的文件(61k).

四 说明

必须说明的是，在原官方的程序中有很多地方提到如GetOverview与GetViewCount等函数。这就涉及到建立栅格金字塔问题，如果其实如果数据不大，或者可以忍受读取，主要就是一种显示数据索引。但作为初学者，我觉得还是不去考虑了，随着学习的深入，以后会有接触。