Merge pull request #41670 from elpaso/bugfix-gh41662-raster-byte-noda…

…ta-diagonal

Set min/max from data type when GDAL stats fail

src/core/providers/gdal/qgsgdalprovider.cpp

@@ -2882,6 +2882,10 @@ QgsRasterBandStats QgsGdalProvider::bandStatistics( int bandNo, int stats, const
     QgsDebugMsgLevel( QStringLiteral( "STDDEV %1" ).arg( myRasterBandStats.stdDev ), 2 );
 #endif
   }
+  else
+  {
+    myRasterBandStats.statsGathered = QgsRasterBandStats::Stats::None;
+  }
 
   mStatistics.append( myRasterBandStats );
   return myRasterBandStats;

src/core/raster/qgsrasterlayer.cpp

@@ -992,6 +992,67 @@ void QgsRasterLayer::computeMinMax( int band,
   if ( limits == QgsRasterMinMaxOrigin::MinMax )
   {
     QgsRasterBandStats myRasterBandStats = mDataProvider->bandStatistics( band, QgsRasterBandStats::Min | QgsRasterBandStats::Max, extent, sampleSize );
+    // Check if statistics were actually gathered, None means a failure
+    if ( myRasterBandStats.statsGathered == QgsRasterBandStats::Stats::None )
+    {
+      // Best guess we can do
+      switch ( mDataProvider->dataType( band ) )
+      {
+        case Qgis::DataType::Byte:
+        {
+          myRasterBandStats.minimumValue = 0;
+          myRasterBandStats.maximumValue = 255;
+          break;
+        }
+        case Qgis::DataType::UInt16:
+        {
+          myRasterBandStats.minimumValue = 0;
+          myRasterBandStats.maximumValue = std::numeric_limits<uint16_t>::max();
+          break;
+        }
+        case Qgis::DataType::UInt32:
+        {
+          myRasterBandStats.minimumValue = 0;
+          myRasterBandStats.maximumValue = std::numeric_limits<uint32_t>::max();
+          break;
+        }
+        case Qgis::DataType::Int16:
+        case Qgis::DataType::CInt16:
+        {
+          myRasterBandStats.minimumValue = std::numeric_limits<int16_t>::lowest();
+          myRasterBandStats.maximumValue = std::numeric_limits<int16_t>::max();
+          break;
+        }
+        case Qgis::DataType::Int32:
+        case Qgis::DataType::CInt32:
+        {
+          myRasterBandStats.minimumValue = std::numeric_limits<int32_t>::lowest();
+          myRasterBandStats.maximumValue = std::numeric_limits<int32_t>::max();
+          break;
+        }
+        case Qgis::DataType::Float32:
+        case Qgis::DataType::CFloat32:
+        {
+          myRasterBandStats.minimumValue = std::numeric_limits<float_t>::lowest();
+          myRasterBandStats.maximumValue = std::numeric_limits<float_t>::max();
+          break;
+        }
+        case Qgis::DataType::Float64:
+        case Qgis::DataType::CFloat64:
+        {
+          myRasterBandStats.minimumValue = std::numeric_limits<double_t>::lowest();
+          myRasterBandStats.maximumValue = std::numeric_limits<double_t>::max();
+          break;
+        }
+        case Qgis::DataType::ARGB32:
+        case Qgis::DataType::ARGB32_Premultiplied:
+        case Qgis::DataType::UnknownDataType:
+        {
+          // Nothing to guess
+          break;
+        }
+      }
+    }
     min = myRasterBandStats.minimumValue;
     max = myRasterBandStats.maximumValue;
   }