Do not persist estimated GDAL metadata

GDAL saves metadata like min and max values into a .aux.xml sidecar file next to raster files. It does this always, even when the calculated values are estimated. In subsequent runs of GDAL processing tools it will use these values as if they were reliable. This patch takes care of deleting newly written .aux.xml files if there is a risk that they include estimated data. Fix #19517 https://issues.qgis.org/issues/19517
qgis · Oct 25, 2018 · 87fddae · 87fddae
1 parent 607cd3e
commit 87fddae
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diff --git a/src/providers/gdal/qgsgdalprovider.cpp b/src/providers/gdal/qgsgdalprovider.cpp
@@ -105,6 +105,7 @@ QgsGdalProvider::QgsGdalProvider( const QString &uri, QgsError error )
     , mYBlockSize( 0 )
     , mGdalBaseDataset( nullptr )
     , mGdalDataset( nullptr )
+    , mStatisticsAreReliable( false )
 {
   mGeoTransform[0] =  0;
   mGeoTransform[1] =  1;
@@ -127,6 +128,7 @@ QgsGdalProvider::QgsGdalProvider( const QString &uri, bool update )
     , mYBlockSize( 0 )
     , mGdalBaseDataset( nullptr )
     , mGdalDataset( nullptr )
+    , mStatisticsAreReliable( false )
 {
   mGeoTransform[0] =  0;
   mGeoTransform[1] =  1;
@@ -240,7 +242,15 @@ QgsGdalProvider::~QgsGdalProvider()
   }
   if ( mGdalDataset )
   {
+    // Check if already a PAM (persistent auxiliary metadata) file exists
+    QString pamFile = dataSourceUri() + QLatin1String( ".aux.xml" );
+    bool pamFileAlreadyExists = QFileInfo( pamFile ).exists();
+
     GDALClose( mGdalDataset );
+
+    // If GDAL created a PAM file right now by using estimated metadata, delete it right away
+    if ( !mStatisticsAreReliable && !pamFileAlreadyExists && QFileInfo( pamFile ).exists() )
+      QFile( pamFile ).remove();
   }
 }
 
@@ -2443,6 +2453,7 @@ QgsRasterBandStats QgsGdalProvider::bandStatistics( int theBandNo, int theStats,
     myerval = GDALComputeRasterStatistics( myGdalBand, bApproxOK,
                                            &pdfMin, &pdfMax, &pdfMean, &pdfStdDev,
                                            progressCallback, &myProg );
+    mStatisticsAreReliable = true;
   }
   else
   {

diff --git a/src/providers/gdal/qgsgdalprovider.h b/src/providers/gdal/qgsgdalprovider.h
@@ -301,6 +301,8 @@ class QgsGdalProvider : public QgsRasterDataProvider, QgsGdalProviderBase
 
     /** \brief sublayers list saved for subsequent access */
     QStringList mSubLayers;
+
+    bool mStatisticsAreReliable;
 };
 
 #endif