在遥感图像处理中，GDAL库不仅能读取和处理大部分的遥感图像数据，而且还能够实现图像处理后将数据保存为图像的功能。
本文就详细介绍如何将内存中的图像数据保存为.tif格式。
首先，遥感数据处理完，保存在一维数组data中，图像的宽和高为width和height，图像有三个波段。在保存时要使图像的每一行对其，保证位数为32的倍数
先上实现的代码，源程序如下：
1 int bytesPerLine=(width*24+31)/8;//字节对齐
2 unsigned char *data=new unsigned char[bytesPerLine*height];
3
4 //图像处理......
5
6 GDALAllRegister();//注册数据集
7 GDALDriver *poDriver;
8 GDALDataset *BiomassDataset;
9 poDriver = GetGDALDriverManager()->GetDriverByName("Gtiff");
10
11 const char *output_file="D:xxxx";
12
13 BiomassDataset=poDriver->Create(output_file,width,height,3,GDT_Byte, NULL);
14
15 int panBandMap [3]= {1,2,3};
16 BiomassDataset->RasterIO(GF_Write,0,0,width,height,data_show_,width,height,GDT_Byte,3,panBandMap,3,bytesPerLine,1);
17
18 GDALClose(BiomassDataset);
19 BiomassDataset=NULL;
20
21
22 delete []data;
23 data=NULL;
这里关键的就是Create和RasterIO两个函数
Create函数的功能为创建一个文件，创建成功就返回一个GDALDataSet类指针对象，然后再使用这个指针对象调用RasterIO向文件内写数据。Create函数的原型：
GDALDataset * GDALDriver::Create ( const char * pszFilename,
int nXSize,
int nYSize,
int nBands,
GDALDataType eType,
char ** papszOptions
)
Parameters:
| pszFilename | the name of the dataset to create. UTF-8 encoded. | |
| nXSize | width of created raster in pixels. | |
| nYSize | height of created raster in pixels. | |
| nBands | number of bands. | |
| eType | type of raster. | |
| papszOptions | list of driver specific control parameters. |
需要注意的是nXSize和nXSize均是值像素的个数，而非字节个数，所以程序中是width和height。文件创建好了，里面数据是空的，下面就往文件里面写图像数据
RasterIO是GDALDataSet类的方法，功能是写数据，函数原型如下：
CPLErr GDALDataset::RasterIO ( GDALRWFlag eRWFlag,
int nXOff,
int nYOff,
int nXSize,
int nYSize,
void * pData,
int nBufXSize,
int nBufYSize,
GDALDataType eBufType,
int nBandCount,
int * panBandMap,
int nPixelSpace,
int nLineSpace,
int nBandSpace
)
Parameters:
| eRWFlag | Either GF_Read to read a region of data, or GF_Write to write a region of data. | |
| nXOff | The pixel offset to the top left corner of the region of the band to be accessed. This would be zero to start from the left side. | |
| nYOff | The line offset to the top left corner of the region of the band to be accessed. This would be zero to start from the top. | |
| nXSize | The width of the region of the band to be accessed in pixels. | |
| nYSize | The height of the region of the band to be accessed in lines. | |
| pData | The buffer into which the data should be read, or from which it should be written. This buffer must contain at least nBufXSize * nBufYSize * nBandCount words of type eBufType. It is organized in left to right,top to bottom pixel order. Spacing is controlled by the nPixelSpace, and nLineSpace parameters. | |
| nBufXSize | the width of the buffer image into which the desired region is to be read, or from which it is to be written. | |
| nBufYSize | the height of the buffer image into which the desired region is to be read, or from which it is to be written. | |
| eBufType | the type of the pixel values in the pData data buffer. The pixel values will automatically be translated to/from the GDALRasterBand data type as needed. | |
| nBandCount | the number of bands being read or written. | |
| panBandMap | the list of nBandCount band numbers being read/written. Note band numbers are 1 based. This may be NULL to select the first nBandCount bands. | |
| nPixelSpace | The byte offset from the start of one pixel value in pData to the start of the next pixel value within a scanline. If defaulted (0) the size of the datatype eBufType is used. | |
| nLineSpace | The byte offset from the start of one scanline in pData to the start of the next. If defaulted (0) the size of the datatype eBufType * nBufXSize is used. | |
| nBandSpace | the byte offset from the start of one bands data to the start of the next. If defaulted (0) the value will be nLineSpace * nBufYSize implying band sequential organization of the data buffer. |
这里的图像数据宽度和高度均是指图像像素点的个数，所以都是width和height。要特别注意最后四个参数。
int* panBandMap：波段的排列顺序，比如RGB，BGR等
int nPixelSpace：写入时相邻像素间的字节数大小，这里每个像素三个波段，因此为3
int nLineSpace：图像相邻行见字节数的大小，这里一行又bytePerLine个字节，因此为bytePerLine
int nBandSpace：写入时相邻波段见字节大小，这里写入的波段都是紧挨着的，因此为1