Reproject by GDAL GDALAutoCreateWarpedVRT in C

Question

I want to re-project an HDF from UTM(WGS84) to sinusoidal（WGS84), so I try to use GDALAutoCreateWarpedVRT to finished it. The code is below:

hSrcDS = (GDALDataset*)GDALOpen("HJ1ACCD1.hdf", GA_ReadOnly);
const char *pszSrcWKT = NULL;
char*  pszDstWKT = NULL;
//pszSrcWKT = ProjectionStr;
pszSrcWKT=GDALGetProjectionRef(hSrcDS);
CPLAssert( pszSrcWKT != NULL &&strlen(pszSrcWKT) > 0 );

OGRSpatialReference oSRS;
oSRS.SetSinusoidal(0,0,0);
oSRS.SetWellKnownGeogCS("WGS84");
oSRS.exportToWkt(&pszDstWKT );

GDALWarpOptions*psWarpOptions = GDALCreateWarpOptions();  
psWarpOptions->dfWarpMemoryLimit=500*1024*1024;

hDstDS=(GDALDataset*)(GDALDataset*)GDALAutoCreateWarpedVRT(hSrcDS,pszSrcWKT,pszDstWKT,GRA_Bilinear ,20,psWarpOptions);
GDALDriver *poDriverTiff;
poDriverTiff=GetGDALDriverManager()->GetDriverByName("GTIFF");
poDriverTiff->CreateCopy("d:\\toto.tif",(GDALDataset*)hDstDS,false,NULL,NULL,NULL);

When I set oSRS.SetSinusoidal(0,0,0)，the result seems good, but the resolution is doubled (from 30 to 60). It's so weird.

Answer 1

According to the API docs for GDALAutoCreateWarpedVRT:

The GDALSuggestedWarpOutput() function is used to determine the bounds and resolution of the output virtual file which should be large enough to include all the input image

There is also a GDALSuggestedWarpOutput2() function to help suggest output file size for a similar set of requirements.