diff --git a/include/osgTerrain/Layer b/include/osgTerrain/Layer
index 39bf2ae92..117731ed5 100644
--- a/include/osgTerrain/Layer
+++ b/include/osgTerrain/Layer
@@ -40,6 +40,8 @@ class OSGTERRAIN_EXPORT Layer : public osg::Object
         
         const Locator* getLocator() const { return _locator.get(); }
 
+        virtual osg::BoundingSphere computeBound() const;
+
     protected:
 
         virtual ~Layer();
diff --git a/include/osgTerrain/Locator b/include/osgTerrain/Locator
index 06190b9ca..21dc65118 100644
--- a/include/osgTerrain/Locator
+++ b/include/osgTerrain/Locator
@@ -33,8 +33,8 @@ class OSGTERRAIN_EXPORT Locator : public osg::Object
         
         META_Object(osgTerrain, Locator);
         
-        virtual bool convertLocalToModel(const osg::Vec3d& /*local*/, osg::Vec3d& /*world*/) { return false; };
-        virtual bool convertModelToWorld(const osg::Vec3d& /*world*/, osg::Vec3d& /*local*/) { return false; };
+        virtual bool convertLocalToModel(const osg::Vec3d& /*local*/, osg::Vec3d& /*world*/) const { return false; }
+        virtual bool convertModelToWorld(const osg::Vec3d& /*world*/, osg::Vec3d& /*local*/) const { return false; }
 
     protected:
 
@@ -62,8 +62,8 @@ public:
     osg::EllipsoidModel* getEllipsoidModel() { return _em.get(); }
     const osg::EllipsoidModel* getEllipsoidModel() const { return _em.get(); }
 
-    bool convertLocalToModel(const osg::Vec3d& local, osg::Vec3d& world);
-    bool convertModelToWorld(const osg::Vec3d& world, osg::Vec3d& local);    
+    bool convertLocalToModel(const osg::Vec3d& local, osg::Vec3d& world) const;
+    bool convertModelToWorld(const osg::Vec3d& world, osg::Vec3d& local) const;    
 
 protected:
 
diff --git a/include/osgTerrain/TerrainNode b/include/osgTerrain/TerrainNode
index cdbda3be6..c34ad69f8 100644
--- a/include/osgTerrain/TerrainNode
+++ b/include/osgTerrain/TerrainNode
@@ -73,6 +73,9 @@ class OSGTERRAIN_EXPORT TerrainNode : public osg::Group
         osg::TransferFunction* getColorTransferFunction() { return _colorTransferFunction.get(); }
         const osg::TransferFunction* getColorTransferFunction() const { return _colorTransferFunction.get(); }
 
+        /** Compute the bounding volume of the terrain by computing the union of the bounding volumes of all layers.*/
+        virtual osg::BoundingSphere computeBound() const;
+
     protected:
 
         virtual ~TerrainNode();
diff --git a/src/osgTerrain/Layer.cpp b/src/osgTerrain/Layer.cpp
index 14bf7fa1f..3e4ca0d4b 100644
--- a/src/osgTerrain/Layer.cpp
+++ b/src/osgTerrain/Layer.cpp
@@ -28,6 +28,36 @@ Layer::~Layer()
 {
 }
 
+osg::BoundingSphere Layer::computeBound() const
+{
+    osg::BoundingSphere bs;
+    if (!getLocator()) return bs;
+
+    osg::Vec3d v;
+    if (getLocator()->convertLocalToModel(osg::Vec3d(0.0,0.0,0.0), v))
+    {
+        bs.expandBy(v);
+    }
+    
+    if (getLocator()->convertLocalToModel(osg::Vec3d(1.0,0.0,0.0), v))
+    {
+        bs.expandBy(v);
+    }
+
+    if (getLocator()->convertLocalToModel(osg::Vec3d(1.0,1.0,0.0), v))
+    {
+        bs.expandBy(v);
+    }
+
+    if (getLocator()->convertLocalToModel(osg::Vec3d(0.0,1.0,0.0), v))
+    {
+        bs.expandBy(v);
+    }
+    
+    return bs;
+}
+
+
 /////////////////////////////////////////////////////////////////////////////
 //
 // ImageLayer
diff --git a/src/osgTerrain/Locator.cpp b/src/osgTerrain/Locator.cpp
index 514269aeb..d6191de70 100644
--- a/src/osgTerrain/Locator.cpp
+++ b/src/osgTerrain/Locator.cpp
@@ -58,7 +58,7 @@ void EllipsoidLocator::setExtents(double longitude, double latitude, double delt
     _height = height;
 }
 
-bool EllipsoidLocator::convertLocalToModel(const osg::Vec3d& local, osg::Vec3d& world)
+bool EllipsoidLocator::convertLocalToModel(const osg::Vec3d& local, osg::Vec3d& world) const
 {
     double longitude = _longitude + local.x() * _deltaLongitude;
     double latitude = _latitude + local.y() * _deltaLatitude;
@@ -70,7 +70,7 @@ bool EllipsoidLocator::convertLocalToModel(const osg::Vec3d& local, osg::Vec3d&
     return true;
 }
 
-bool EllipsoidLocator::convertModelToWorld(const osg::Vec3d& world, osg::Vec3d& local)
+bool EllipsoidLocator::convertModelToWorld(const osg::Vec3d& world, osg::Vec3d& local) const
 {
     double longitude, latitude, height;
 
diff --git a/src/osgTerrain/TerrainNode.cpp b/src/osgTerrain/TerrainNode.cpp
index d227cd452..66fa6c915 100644
--- a/src/osgTerrain/TerrainNode.cpp
+++ b/src/osgTerrain/TerrainNode.cpp
@@ -75,3 +75,14 @@ void TerrainNode::setColorTransferFunction(osg::TransferFunction* tf)
 {
     _colorTransferFunction = tf;
 }
+
+osg::BoundingSphere TerrainNode::computeBound() const
+{
+    osg::BoundingSphere bs;
+    
+    if (_elevationLayer.valid()) bs.expandBy(_elevationLayer->computeBound());
+
+    if (_colorLayer.valid()) bs.expandBy(_colorLayer->computeBound());
+
+    return bs;
+}