[gdal-dev] GeoTIFFs and GetStatistics

[Rory O'Connor]

Hello,

Does the TIFF driver support the SetStatistics function? I work with
~4GB TIFF files and it takes a significant amount of time to call
ComputeStatistics. Everytime I open a file or create one it takes about 10
minutes to calculate the statistics, which would be OK if it was a one time
only thing. The statistics are seemingly not cached in the meta
data or the Xml file even if the file was opened as a PAM dataset. Also it
didn't make a difference if the dataset was opened with read-only or update
permissions.

Here is a snippet of my code:

    int bForce = FALSE;
    int approxOK = TRUE;
    CPLErr err = poBand->GetStatistics (approxOK, bForce, minValue,
maxValue, pMean, pStdDev);

    if ( err != CE_None )
    {
        // Stats not cached, recompute them
        // BPS - using ApproxOK does not seem to obey the NoDataValue (mean
shifted toward 0)
        // also behaves differently if we just made overviews or already had
them
        // But it's soooooo much faster than recalcing full stats on a big
file
        poBand->ComputeStatistics (FALSE, minValue, maxValue, pMean,
pStdDev, NULL, NULL);
        poBand->SetStatistics (*minValue, *maxValue, *pMean, *pStdDev);
    }

BTW, thanks for the great product. Overall it has been a joy to use so far.

Regards,
Rory
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