Iam writing a custom GDAL driver (RBD format). I was able to display the base
image (overview no = -1) but for a big image(5 GB) it takes huge amount of
time.
So i was displaying its overview (ex; image has 3 overviews and i always
displays the last overview). In this case ArcGIS 10 displays image fastly
since its a overview.
But i require help on dynamically displaying the overviews (i.e 0,1,2 or 3)
when the overview image is Zoomed in/out.
IReadBlock() gets invoked only for the first time when displaying the
overview image.
Here is the code written in IReadBlock()
CPLErr RBDRasterBand::IReadBlock( int nBlockXOff, int nBlockYOff, void *
pImage )
{
RBDDataset *poGDS = (RBDDataset *) poDS;
long nBand = 0, nOVNumber = 0;
unsigned long nMinX = 0, nMaxX = 0, nMinY = 0, nMaxY = 0;
long nTileSizeX = 0, nTileSizeY = 0;
long nBandFlag;
long nBufferSize;
ICTM *pICTM;
pICTM = poGDS->pziiFile->pICTM;
nOVNumber = poGDS ->pziiFile ->nNumberOfOVs - 1; // if it has overviews
0,1,2 it dispalys 2 Ov.
nBand = this->nBand;
if(-1 == nOVNumber)
{
nTileSizeX = poGDS->pziiFile->nXTileSize;
nTileSizeY = poGDS->pziiFile->nYTileSize;
}
else
{
nTileSizeX =
poGDS->pziiFile->pzii_LayerOVInfo[nOVNumber]->nXTileSize;
nTileSizeY =
poGDS->pziiFile->pzii_LayerOVInfo[nOVNumber]->nYTileSize;
}
//Get the RowMin, RowMax, ColMin and ColMax values
nMinX = nBlockXOff * nTileSizeX;
nMinY = nBlockYOff * nTileSizeY;
nMaxX = nMinX + nTileSizeX-1;//Zero Index
nMaxY = nMinY + nTileSizeY-1;//Zero Index
//Set the band flag
if(nBand == 1)
nBandFlag = RED_FLAG;
else if(nBand == 2)
nBandFlag = GREEN_FLAG;
else if(nBand == 3)
nBandFlag = BLUE_FLAG;
//Calculate buffer size
nBufferSize = (nMaxX + 1 - nMinX) * (nMaxY + 1 - nMinY) *
poGDS->pziiFile->nNumberOfBytesPerBand;
////Call RenderRequestByOV on CTM object - it is our 3 part method which
fills the image buffer.
pICTM->RenderRequestByOV(nOVNumber,nBandFlag,nMinX,nMinY,nMaxX,nMaxY,&nBufferSize,(unsigned
char*)pImage,FALSE,0);
return CE_None ;
--
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