convert GDAL no data value to a value representable by data type, fixes #3840

Author: blazek

src/core/raster/qgsraster.cpp

@@ -53,4 +53,24 @@ QgsRaster::ContrastEnhancementLimits QgsRaster::contrastEnhancementLimitsFromStr
   return ContrastEnhancementNone;
 }
 
-
+double QgsRaster::representableValue( double value, QGis::DataType dataType )
+{
+  switch ( dataType )
+  {
+    case QGis::Byte:
+      return static_cast<quint8>( value );
+    case QGis::UInt16:
+      return static_cast<quint16>( value );
+    case QGis::Int16:
+      return static_cast<qint16>( value );
+    case QGis::UInt32:
+      return static_cast<quint32>( value );
+    case QGis::Int32:
+      return static_cast<qint32>( value );
+    case QGis::Float32:
+      return static_cast<float>( value );
+    default:
+      break;
+  }
+  return value;
+}

src/core/raster/qgsraster.h

@@ -20,6 +20,8 @@
 
 #include <QString>
 
+#include "qgis.h"
+
 /** \ingroup core
  * Raster namespace.
  */
@@ -108,6 +110,12 @@ class CORE_EXPORT QgsRaster
     static QString contrastEnhancementLimitsAsString( QgsRaster::ContrastEnhancementLimits theLimits );
     static ContrastEnhancementLimits contrastEnhancementLimitsFromString( QString theLimits );
 
+    /** Get value representable by given data type.
+     * Supported are numerical types Byte, UInt16, Int16, UInt32, Int32, Float32, Float64.
+     * @param value
+     * @param dataType
+     * @note added in version 2.1 */
+    static double representableValue( double value, QGis::DataType dataType );
 };
 
 #endif

src/providers/gdal/qgsgdalprovider.cpp

@@ -2411,6 +2411,10 @@ void QgsGdalProvider::initBaseDataset()
     if ( isValid )
     {
       QgsDebugMsg( QString( "GDALGetRasterNoDataValue = %1" ).arg( myNoDataValue ) ) ;
+      // The no data value double may be non representable by data type, it can result
+      // in problems if that value is used to represent additional user defined no data
+      // see #3840
+      myNoDataValue = QgsRaster::representableValue( myNoDataValue, dataTypeFromGdal( myGdalDataType ) );
       mSrcNoDataValue.append( myNoDataValue );
       mSrcHasNoDataValue.append( true );
       mUseSrcNoDataValue.append( true );

src/providers/wcs/qgswcsprovider.cpp

@@ -303,6 +303,7 @@ QgsWcsProvider::QgsWcsProvider( QString const &uri )
     if ( isValid )
     {
       QgsDebugMsg( QString( "GDALGetRasterNoDataValue = %1" ).arg( myNoDataValue ) ) ;
+      myNoDataValue = QgsRaster::representableValue( myNoDataValue, dataTypeFromGdal( myGdalDataType ) );
       mSrcNoDataValue.append( myNoDataValue );
       mSrcHasNoDataValue.append( true );
       mUseSrcNoDataValue.append( true );