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影像读取 并缩放
读取大影像某一部分，并缩放到指定大小，我们有时会用如下代码：
#include "gdal.h" #include "gdal_priv.h" #include "gdalwarper.h" void main() { GDALAllRegister(); CPLSetConfigOption("GDAL_FILENAME_IS_UTF8","NO");//support Chinese GDALDataset* readDataSet = (GDALDataset*)GDALOpen(inputFile.c_str(),GA_ReadOnly); if (readDataSet == NULL ) { return; } int width = readDataSet->GetRasterXSize(); int height = readDataSet->GetRasterYSize(); int bandCount = readDataSet->GetRasterCount(); int tilesize = 50; unsigned char* data = new unsigned char[tilesize*tilesize*bandCount]; if (readDataSet->RasterIO(GDALRWFlag::GF_Read,0,0,width,height,data,tilesize,tilesize,GDT_Byte,bandCount,NULL,0,0,0)==CPLErr::CE_Failure) { delete readDataSet;readDataSet=NULL; delete data; return; }
}
让我们从RasterIO接口谈起，跟其中代码，得知
1、从影像金字塔取数据。根据缩小到的TileSize，它会从影像金字塔中取相应层级的数据。
2、取到数据后，会进行最近邻插值。
由于最近邻插值效果不佳，会导致得到的数据，都是相应的噪声，麻点现象。
GDAL从2.0版本支持RasterIO接口进行插值算法的配置，仅仅进行简单的配置，就可以解决这个问题。
GDALRasterIOExtraArg exterArg; INIT_RASTERIO_EXTRA_ARG(exterArg); exterArg.eResampleAlg = GDALRIOResampleAlg::GRIORA_Bilinear; readDataSet->RasterIO(GDALRWFlag::GF_Read,0,0,width,height,data,tilesize,tilesize,GDT_Byte,bandCount,NULL,0,0,0,&exterArg);
如下写出进行验证
GDALDriver *pDriver; pDriver = GetGDALDriverManager()->GetDriverByName("GTiff"); GDALDataset* gdalDataset; gdalDataset = pDriver->Create(outputFile.c_str(),tilesize,tilesize,bandCount,GDT_Byte,NULL); gdalDataset->RasterIO(GF_Write,0,0,tilesize,tilesize,data,tilesize,tilesize,GDT_Byte,bandCount,NULL,0,0,0); GDALClose(gdalDataset); gdalDataset = NULL;
参考：https://trac.osgeo.org/gdal/wiki/rfc51_rasterio_resampling_progress
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原文地址：http://www.cnblogs.com/geospatial/p/5630630.html
