diff --git a/include/osgTerrain/Layer b/include/osgTerrain/Layer
index e2c1613e5..534577333 100644
--- a/include/osgTerrain/Layer
+++ b/include/osgTerrain/Layer
@@ -320,7 +320,7 @@ class OSGTERRAIN_EXPORT ProxyLayer : public Layer
         virtual void close() {}
 
         /** Extract an ImageLayer from the ProxyLayer.*/
-        virtual ImageLayer* extractImageLayer(unsigned int /*minX*/, unsigned int /*minY*/, unsigned int /*maxX*/, unsigned int /*maxY*/) { return 0; }
+        virtual ImageLayer* extractImageLayer(unsigned int /*sourceMinX*/, unsigned int /*sourceMinY*/, unsigned int /*sourceMaxX*/, unsigned int /*sourceMaxY*/, unsigned int /*targetWidth*/=0, unsigned int /*targetHeight*/=0) { return 0; }
 
     protected:
 
diff --git a/src/osgPlugins/gdal/DataSetLayer.cpp b/src/osgPlugins/gdal/DataSetLayer.cpp
index 2fa240d92..386f14548 100644
--- a/src/osgPlugins/gdal/DataSetLayer.cpp
+++ b/src/osgPlugins/gdal/DataSetLayer.cpp
@@ -70,11 +70,11 @@ unsigned int DataSetLayer::getNumRows() const
     return _dataset!=0 ? _dataset->GetRasterYSize() : 0;
 }
 
-osgTerrain::ImageLayer* DataSetLayer::extractImageLayer(unsigned int minX, unsigned int minY, unsigned int maxX, unsigned int maxY)
+osgTerrain::ImageLayer* DataSetLayer::extractImageLayer(unsigned int sourceMinX, unsigned int sourceMinY, unsigned int sourceMaxX, unsigned int sourceMaxY, unsigned int targetWidth, unsigned int targetHeight)
 {
-    if (!_dataset || maxX<minX || maxY<minY) return 0;
+    if (!_dataset || sourceMaxX<sourceMinX || sourceMaxY<sourceMinY) return 0;
 
-    osg::notify(osg::NOTICE)<<"DataSetLayer::extractImageLayer("<<minX<<", "<<minY<<", "<<maxX<<", "<<maxY<<") not yet implemented"<<std::endl;
+    osg::notify(osg::NOTICE)<<"DataSetLayer::extractImageLayer("<<sourceMinX<<", "<<sourceMinY<<", "<<sourceMaxX<<", "<<sourceMaxY<<", target:"<<targetWidth<<", "<<targetHeight<<") not yet implemented"<<std::endl;
 
     return 0;
 }
diff --git a/src/osgPlugins/gdal/DataSetLayer.h b/src/osgPlugins/gdal/DataSetLayer.h
index aee73fc2a..f7ff1c358 100644
--- a/src/osgPlugins/gdal/DataSetLayer.h
+++ b/src/osgPlugins/gdal/DataSetLayer.h
@@ -43,7 +43,7 @@ class DataSetLayer : public osgTerrain::ProxyLayer
 
         virtual unsigned int getNumRows() const;
 
-        virtual osgTerrain::ImageLayer* extractImageLayer(unsigned int minX, unsigned int minY, unsigned int maxX, unsigned int maxY);
+        virtual osgTerrain::ImageLayer* extractImageLayer(unsigned int sourceMinX, unsigned int sourceMinY, unsigned int sourceMaxX, unsigned int sourceMaxY, unsigned int targetWidth=0, unsigned int targetHeight=0);
 
     protected: