AE + GDAL实现影像按标准图幅分割（上）

　　最近有个项目，其中有个功能是要将遥感影像按标准图幅分割，一开始用AE的接口，慢的让人抓狂，就改用GDAL，速度提升很大。我主要通过http://blog.csdn.net/liminlu0314/学习GDAL。本篇主要记录GDAL实现分割的代码，下篇用AE写个demo。

　　

 int CutImageByGDAL(const char* pszInFile,const char* pszOutFile,double XMin,double XMax,double YMin,double YMax,const char* pszFormat="GTiff")
 {
     int iSrcXOffset=,iSrcYOffset=;
     int iDstXOffset=,iDstYOffset=;
     int ivXSize=,ivYSize=;
     int xSize=,ySize=;  //结果影像的大小
     double fSrcXMin=XMin,fSrcYMax=YMax;

     GDALAllRegister();
     CPLSetConfigOption("GDAL_FILENAME_IS_UTF8","NO");
     GDALDataset * pSrcDS = (GDALDataset*) GDALOpen(pszInFile, GA_ReadOnly);
     if (pSrcDS == NULL)
     {
         return -;
         //return "未能打开影像文件";
     }
     try
     {
         int iBandCount = pSrcDS->GetRasterCount();
         const char* pszWkt = pSrcDS->GetProjectionRef();  //影像的坐标系
         GDALDataType dT = pSrcDS->GetRasterBand()->GetRasterDataType(); //影像的数据类型

         double adfGeoTransform[] = {};
         double newGeoTransform[] = {};
                 //获取影像的坐标转换参数
         pSrcDS->GetGeoTransform(adfGeoTransform);
                 //结果影像的坐标转换参数
         memcpy(newGeoTransform, adfGeoTransform, sizeof(double)*);
         newGeoTransform[]=XMin;
         newGeoTransform[]=YMax;

         //地理坐标转换为影像上的像素坐标
 Projection2ImageRowCol(adfGeoTransform,XMin,YMax,iSrcXOffset,iSrcYOffset);
         Projection2ImageRowCol(adfGeoTransform,XMax,YMin,xSize,ySize);
         xSize=xSize-iSrcXOffset;
         ySize=ySize-iSrcYOffset;
         ivXSize=xSize;
         ivYSize=ySize;

         GDALDataset* pDstDS;
             GDALDriver *pDriver = GetGDALDriverManager()->GetDriverByName(pszFormat);
             if (pDriver == NULL)
             {
                 GDALClose((GDALDatasetH) pSrcDS);
                 return -;
                 //return "未能创建影像文件驱动";
             }
             //GDALDataset*
             pDstDS = pDriver->Create(pszOutFile, xSize, ySize, iBandCount, dT, NULL);
             if (pDstDS == NULL)
             {
                 GDALClose((GDALDatasetH) pSrcDS);
                 return -;
                 //return "未能创建影像文件";
             }
             pDstDS->SetGeoTransform(newGeoTransform);
                         //设置影像坐标系
             pDstDS->SetProjection(pszWkt);  

         //边界处理
         //判断切割范围，使其不超过原始影像范围
         //如果切割范围超过原始影像，会导致结果影像像素值全是NoData
         if(XMin<adfGeoTransform[])
             fSrcXMin=adfGeoTransform[];
         if(YMax>adfGeoTransform[])
             fSrcYMax=adfGeoTransform[];

         Projection2ImageRowCol(adfGeoTransform,fSrcXMin,fSrcYMax,iSrcXOffset,iSrcYOffset);
         Projection2ImageRowCol(newGeoTransform,fSrcXMin,fSrcYMax,iDstXOffset,iDstYOffset);

         if(iSrcXOffset+xSize>pSrcDS->GetRasterXSize())
             ivXSize=pSrcDS->GetRasterXSize()-iSrcXOffset;
         if(iDstXOffset+ivXSize>pDstDS->GetRasterXSize())
             ivXSize=pDstDS->GetRasterXSize()-iDstXOffset;

         if(iSrcYOffset+ySize>pSrcDS->GetRasterYSize())
             ivYSize=pSrcDS->GetRasterYSize()-iSrcYOffset;
         if(iDstYOffset+ivYSize>pDstDS->GetRasterYSize())
             ivYSize=pDstDS->GetRasterYSize()-iDstYOffset;

         void * pMemData;
         switch(dT)
         {
         case GDT_Byte:
             pMemData=new char[xSize*ySize*iBandCount];
             break;
         case GDT_UInt16:
         case GDT_Int16:
         case GDT_CInt16:
             pMemData=new int[xSize*ySize*iBandCount];
             break;
         case GDT_UInt32:
         case GDT_Int32:
         case GDT_Float32:
         case GDT_CInt32:
         case GDT_CFloat32:
             pMemData=new float[xSize*ySize*iBandCount];
             break;
         case GDT_Unknown:
         case GDT_Float64:
         case GDT_CFloat64:
             pMemData=new double[xSize*ySize*iBandCount];
             break;
         }
 　　　　
         pSrcDS->RasterIO(GF_Read,iSrcXOffset,iSrcYOffset,ivXSize,ivYSize,pMemData,ivXSize,ivYSize,dT,iBandCount,,,,);
         pDstDS->RasterIO(GF_Write,iDstXOffset,iDstYOffset,ivXSize,ivYSize,pMemData,ivXSize,ivYSize,dT,iBandCount,,,,);

         GDALClose((GDALDatasetH) pSrcDS);
         GDALClose((GDALDatasetH) pDstDS);
         free(pMemData);

         return ;
         //return "完成";
     }
     catch(const char* excep)
     {
         if(pSrcDS!=NULL)
             GDALClose((GDALDatasetH) pSrcDS);
         return ;
     }
 }

　　

Projection2ImageRowCol是把地理坐标转换为影像像素坐标的函数，实现如下

 bool Projection2ImageRowCol(double *adfGeoTransform, double dProjX, double dProjY, int &iCol, int &iRow)
 {
     try
     {
         double dTemp = adfGeoTransform[]*adfGeoTransform[] - adfGeoTransform[]*adfGeoTransform[];
         double dCol = 0.0, dRow = 0.0;
         dCol = (adfGeoTransform[]*(dProjX - adfGeoTransform[]) -
             adfGeoTransform[]*(dProjY - adfGeoTransform[])) / dTemp +0.5;
         dRow = (adfGeoTransform[]*(dProjY - adfGeoTransform[]) -
             adfGeoTransform[]*(dProjX - adfGeoTransform[])) / dTemp +0.5;  

         iCol = static_cast<int>(dCol);
         iRow = static_cast<int>(dRow);
         return true;
     }
     catch(...)
     {
         return false;
     }
 }