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:
int bytesPerLine=(width*+)/;//字节对齐
unsigned char *data=new unsigned char[bytesPerLine*height]; //图像处理...... GDALAllRegister();//注册数据集
GDALDriver *poDriver;
GDALDataset *BiomassDataset;
poDriver = GetGDALDriverManager()->GetDriverByName("Gtiff"); const char *output_file="D:\xxxx"; BiomassDataset=poDriver->Create(output_file,width,height,,GDT_Byte, NULL); int panBandMap []= {,,};
BiomassDataset->RasterIO(GF_Write,,,width,height,data_show_,width,height,GDT_Byte,,panBandMap,,bytesPerLine,); GDALClose(BiomassDataset);
BiomassDataset=NULL; delete []data;
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