fix when GDALGetRasterScale returns 0 (gdal 2.3 affected for some dat…

…asets)

(cherry picked from commit 7a12f11)

src/providers/gdal/qgsgdalprovider.cpp

@@ -1280,7 +1280,9 @@ double QgsGdalProvider::bandScale( int bandNo ) const
   GDALRasterBandH myGdalBand = getBand( bandNo );
   int bGotScale;
   double myScale = GDALGetRasterScale( myGdalBand, &bGotScale );
-  if ( bGotScale )
+
+  // if scale==0, ignore both scale and offset
+  if ( bGotScale && !qgsDoubleNear( myScale, 0.0 ) )
     return myScale;
   else
     return 1.0;
@@ -1293,6 +1295,13 @@ double QgsGdalProvider::bandOffset( int bandNo ) const
     return 0.0;
 
   GDALRasterBandH myGdalBand = getBand( bandNo );
+
+  // if scale==0, ignore both scale and offset
+  int bGotScale;
+  double myScale = GDALGetRasterScale( myGdalBand, &bGotScale );
+  if ( bGotScale && qgsDoubleNear( myScale, 0.0 ) )
+    return 0.0;
+
   int bGotOffset;
   double myOffset = GDALGetRasterOffset( myGdalBand, &bGotOffset );
   if ( bGotOffset )

tests/src/providers/testqgsgdalprovider.cpp

@@ -56,6 +56,7 @@ class TestQgsGdalProvider : public QObject
     void bandNameNoDescription(); // test band name for when no description or tags available (#16047)
     void bandNameWithDescription(); // test band name for when description available (#16047)
     void interactionBetweenRasterChangeAndCache(); // test that updading a raster invalidates the GDAL dataset cache (#20104)
+    void scale0(); //test when data has scale 0 (#20493)
 
   private:
     QString mTestDataDir;
@@ -346,5 +347,16 @@ void TestQgsGdalProvider::interactionBetweenRasterChangeAndCache()
   delete provider;
 }
 
+void TestQgsGdalProvider::scale0()
+{
+  QString raster = QStringLiteral( TEST_DATA_DIR ) + "/raster/scale0ingdal23.tif";
+  QgsDataProvider *provider = QgsProviderRegistry::instance()->createProvider( QStringLiteral( "gdal" ), raster, QgsDataProvider::ProviderOptions() );
+  QgsRasterDataProvider *rp = dynamic_cast< QgsRasterDataProvider * >( provider );
+  QVERIFY( rp );
+  QCOMPARE( rp->bandScale( 1 ), 1.0 );
+  QCOMPARE( rp->bandOffset( 1 ), 0.0 );
+  delete provider;
+}
+
 QGSTEST_MAIN( TestQgsGdalProvider )
 #include "testqgsgdalprovider.moc"