Convenience API call to create empty raster file

Author: wonder-sk

python/core/raster/qgsrasterfilewriter.sip

@@ -29,6 +29,16 @@ class QgsRasterFileWriter
 
     QgsRasterFileWriter( const QString& outputUrl );
 
+    /** Create a raster file with one band without initializing the pixel data.
+     * @note Does not work with tiled mode enabled.
+     * @returns true when the raster has been created successfully
+     * @note added in QGIS 3.0
+     */
+    bool createOneBandRaster( Qgis::DataType dataType,
+                              int width, int height,
+                              const QgsRectangle& extent,
+                              const QgsCoordinateReferenceSystem& crs );
+
     /** Write raster file
         @param pipe raster pipe
         @param nCols number of output columns

src/core/raster/qgsrasterfilewriter.cpp

@@ -29,6 +29,21 @@
 #include <QTextStream>
 #include <QMessageBox>
 
+bool QgsRasterFileWriter::createOneBandRaster( Qgis::DataType dataType, int width, int height, const QgsRectangle &extent, const QgsCoordinateReferenceSystem &crs )
+{
+  if ( mTiledMode )
+    return false;  // does not make sense with tiled mode
+
+  double pixelSize;
+  double geoTransform[6];
+  globalOutputParameters( extent, width, height, geoTransform, pixelSize );
+
+  QgsRasterDataProvider* destProvider = initOutput( width, height, crs, geoTransform, 1, dataType, QList<bool>(), QList<double>() );
+  bool res = destProvider != nullptr;
+  delete destProvider;
+  return res;
+}
+
 QgsRasterFileWriter::QgsRasterFileWriter( const QString& outputUrl )
     : mMode( Raw )
     , mOutputUrl( outputUrl )

src/core/raster/qgsrasterfilewriter.h

@@ -55,6 +55,16 @@ class CORE_EXPORT QgsRasterFileWriter
 
     QgsRasterFileWriter( const QString& outputUrl );
 
+    /** Create a raster file with one band without initializing the pixel data.
+     * @note Does not work with tiled mode enabled.
+     * @returns true when the raster has been created successfully
+     * @note added in QGIS 3.0
+     */
+    bool createOneBandRaster( Qgis::DataType dataType,
+                              int width, int height,
+                              const QgsRectangle& extent,
+                              const QgsCoordinateReferenceSystem& crs );
+
     /** Write raster file
         @param pipe raster pipe
         @param nCols number of output columns

tests/src/core/testqgsrasterfilewriter.cpp

@@ -47,6 +47,7 @@ class TestQgsRasterFileWriter: public QObject
     void cleanup() {} // will be called after every testfunction.
 
     void writeTest();
+    void testCreateOneBandRaster();
   private:
     bool writeTest( const QString& rasterName );
     void log( const QString& msg );
@@ -178,6 +179,31 @@ bool TestQgsRasterFileWriter::writeTest( const QString& theRasterName )
   return ok;
 }
 
+void TestQgsRasterFileWriter::testCreateOneBandRaster()
+{
+  // generate unique filename (need to open the file first to generate it)
+  QTemporaryFile tmpFile;
+  tmpFile.open();
+  tmpFile.close();
+  QString filename = tmpFile.fileName();
+
+  QgsRectangle extent( 106.7, -6.2, 106.9, -6.1 );
+  int width = 200, height = 100;
+
+  QgsRasterFileWriter writer( filename );
+  bool res = writer.createOneBandRaster( Qgis::Byte, width, height, extent, QgsCoordinateReferenceSystem( "EPSG:4326" ) );
+  QVERIFY( res );
+
+  QgsRasterLayer* rlayer = new QgsRasterLayer( filename, "tmp", "gdal" );
+  QVERIFY( rlayer->isValid() );
+  QCOMPARE( rlayer->width(), width );
+  QCOMPARE( rlayer->height(), height );
+  QCOMPARE( rlayer->extent(), extent );
+  QCOMPARE( rlayer->bandCount(), 1 );
+  QCOMPARE( rlayer->dataProvider()->dataType( 1 ), Qgis::Byte );
+}
+
+
 void TestQgsRasterFileWriter::log( const QString& msg )
 {
   mReport += msg + "<br>";