GDAL 遙感圖像處理後的數據保存爲圖像文件的實現方法

在遙感圖像處理中，GDAL庫不只能讀取和處理大部分的遙感圖像數據，並且還可以實現圖像處理後將數據保存爲圖像的功能。

 本文就詳細介紹如何將內存中的圖像數據保存爲.tif格式。

 首先，遙感數據處理完，保存在一維數組data中，圖像的寬和高爲width和height，圖像有三個波段。在保存時要使圖像的每一行對其，保證位數爲32的倍數

 先上實現的代碼，源程序以下：

 1 int bytesPerLine=(width*24+31)/8;//字節對齊 
 2 unsigned char *data=new unsigned char[bytesPerLine*height];  3   
 4 //圖像處理...... 
 5   
 6 GDALAllRegister();//註冊數據集 
 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;  

這裏關鍵的就是Create和RasterIO兩個函數

 Create函數的功能爲建立一個文件，建立成功就返回一個GDALDataSet類指針對象，而後再使用這個指針對象調用RasterIO向文件內寫數據。Create函數的原型：

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.

 

 

 

 

 

 

須要注意的是nXSize和nXSize均是值像素的個數，而非字節個數，因此程序中是width和height。文件建立好了，裏面數據是空的，下面就往文件裏面寫圖像數據

 RasterIO是GDALDataSet類的方法，功能是寫數據，函數原型以下：

 

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.

這裏的圖像數據寬度和高度均是指圖像像素點的個數，因此都是width和height。要特別注意最後四個參數。

int* panBandMap：波段的排列順序，好比RGB，BGR等

int nPixelSpace：寫入時相鄰像素間的字節數大小，這裏每一個像素三個波段，所以爲3

int nLineSpace：圖像相鄰行見字節數的大小，這裏一行又bytePerLine個字節，所以爲bytePerLine

int nBandSpace：寫入時相鄰波段見字節大小，這裏寫入的波段都是緊挨着的，所以爲1