[Gdal-dev] JP2MrSID internal overviews problem

[Sheykhet, Rostic]

Hi all,

I am trying to access JPEG 2000 internal overview data. gdal_info
reports that there are 12 overviews in the file.  When I try 

band = parentBand->GetOverview(nOverview);

/*
     ************************************************************
     *** Debugger information for the returned overview band ****
     ************************************************************
	nBand	1	int
	nRasterXSize	2048	int
	nRasterYSize	2048	int
	eDataType	GDT_Byte	GDALDataType
	eAccess		GA_ReadOnly	GDALAccess
	nBlockXSize	2048	int
	nBlockYSize	128	int
	nBlocksPerRow	0	int
	nBlocksPerColumn	0	int
	bSubBlockingActive	0	int
	nSubBlocksPerRow	0	int
	nSubBlocksPerColumn	0	int
+	papoBlocks	0x00000000	GDALRasterBlock * *
	nBlockReads	0	int
	bForceCachedIO	0	int
*/


CPLErr err = band->RasterIO(GF_Read, 0, 0, 750, 750,
&destBuf[destOffset], 
                            600, 600, GDT_Byte, 0, 0);
//err = CE_Failure
// CPLGetLastErrorMsg() = 
//"MrSIDRasterBand::IRasterIO(): Failed to load image. invalid or empty
scene speficied [50013]"

I've looked at the code and it looks like it attempts to determine the
best overview to use 
whithin the  RasterIO() call.  What are the rules for specifying
overviews explicitly vs. letting the GDAL handle them?  

Thanks a lot

Rostic