Improved the panning support, and added s/getRotationMode(..) to allow

users flip between a trackball rotation style and an azim,elevation style.

include/osgGA/TerrainManipulator

@@ -27,6 +27,17 @@ class OSGGA_EXPORT TerrainManipulator : public MatrixManipulator
 
         virtual const char* className() const { return "Terrain"; }
 
+
+        enum RotationMode 
+        {
+            ELEVATION_AZIM_ROLL,
+            ELEVATION_AZIM,
+        };
+        
+        void setRotationMode(RotationMode mode);
+        RotationMode getRotationMode() const { return _rotationMode; }
+
+
         /** set the minimum distance (as ratio) the eye point can be zoomed in towards the
             center before the center is pushed forward.*/        
         void setMinimumZoomScale(float minimumZoomScale) { _minimumZoomScale=minimumZoomScale; }
@@ -34,6 +45,7 @@ class OSGGA_EXPORT TerrainManipulator : public MatrixManipulator
         /** get the minimum distance (as ratio) the eye point can be zoomed in */
         float getMinimumZoomScale() const { return _minimumZoomScale; }
 
+
         /** set the position of the matrix manipulator using a 4x4 Matrix.*/
         virtual void setByMatrix(const osg::Matrixd& matrix);
 
@@ -100,20 +112,26 @@ class OSGGA_EXPORT TerrainManipulator : public MatrixManipulator
             If speed is below a threshold then return false, otherwise return true.*/
         bool isMouseMoving();
 
+
+        void clampOrientation();
+
+
         // Internal event stack comprising last three mouse events.
         osg::ref_ptr<const GUIEventAdapter> _ga_t1;
         osg::ref_ptr<const GUIEventAdapter> _ga_t0;
 
-        osg::ref_ptr<osg::Node>       _node;
+        osg::ref_ptr<osg::Node> _node;
 
-        float _modelScale;
-        float _minimumZoomScale;
+        float                   _modelScale;
 
-        bool _thrown;
+        RotationMode            _rotationMode;
+        float                   _minimumZoomScale;
+
+        bool                    _thrown;
         
-        osg::CoordinateFrame _coordinateFrame;        
-        osg::Quat   _rotation;
-        float       _distance;
+        osg::CoordinateFrame    _coordinateFrame;        
+        osg::Quat               _rotation;
+        float                   _distance;
 
 };