Backport of smizunos patch that fixes #1540

git-svn-id: http://svn.osgeo.org/qgis/branches/Version-1_0@10593 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: mhugent

src/gui/qgsmapcanvas.cpp

@@ -418,23 +418,25 @@ void QgsMapCanvas::saveAsImage( QString theFileName, QPixmap * theQPixmap, QStri
   //create a world file to go with the image...
   QgsRectangle myRect = mMapRenderer->extent();
   QString myHeader;
+  // note: use 17 places of precision for all numbers output
   //Pixel XDim
-  myHeader += QString::number( mapUnitsPerPixel() ) + "\r\n";
+  myHeader += QString::number( mapUnitsPerPixel(), 'g', 17 ) + "\r\n";
   //Rotation on y axis - hard coded
   myHeader += "0 \r\n";
   //Rotation on x axis - hard coded
   myHeader += "0 \r\n";
   //Pixel YDim - almost always negative - see
   //http://en.wikipedia.org/wiki/World_file#cite_note-2
-  myHeader += "-" + QString::number( mapUnitsPerPixel() ) + "\r\n";
-  //Origin X (top left corner)
-  myHeader += QString::number( myRect.xMinimum() ) + "\r\n";
-  //Origin Y (top left corner)
-  myHeader += QString::number( myRect.yMaximum() ) + "\r\n";
+  myHeader += "-" + QString::number( mapUnitsPerPixel(), 'g', 17 ) + "\r\n";
+  //Origin X (center of top left cell)
+  myHeader += QString::number( myRect.xMinimum() + ( mapUnitsPerPixel() / 2 ), 'g', 17 ) + "\r\n";
+  //Origin Y (center of top left cell)
+  myHeader += QString::number( myRect.yMaximum() - ( mapUnitsPerPixel() / 2 ), 'g', 17 ) + "\r\n";
   QFileInfo myInfo  = QFileInfo( theFileName );
-  QString myWorldFileName = myInfo.absolutePath() + QDir::separator() + myInfo.baseName() + "." + theFormat + "w";
+  // allow dotted names
+  QString myWorldFileName = myInfo.absolutePath() + QDir::separator() + myInfo.completeBaseName() + "." + theFormat + "w";
   QFile myWorldFile( myWorldFileName );
-  if ( !myWorldFile.open( QIODevice::WriteOnly | QIODevice::Text ) )
+  if ( !myWorldFile.open( QIODevice::WriteOnly ) )	//don't use QIODevice::Text
   {
     return;
   }