diff --git a/VisualStudio/osgSim/osgSim.dsp b/VisualStudio/osgSim/osgSim.dsp
index 8ebf7f9d2..386195051 100644
--- a/VisualStudio/osgSim/osgSim.dsp
+++ b/VisualStudio/osgSim/osgSim.dsp
@@ -167,6 +167,10 @@ SOURCE=..\..\src\osgSim\DOFTransform.cpp
 # End Source File
 # Begin Source File
 
+SOURCE=..\..\src\osgSim\HeightAboveTerrain.cpp
+# End Source File
+# Begin Source File
+
 SOURCE=..\..\src\osgSim\Impostor.cpp
 # End Source File
 # Begin Source File
@@ -195,6 +199,10 @@ SOURCE=..\..\src\osgSim\LightPointNode.cpp
 # End Source File
 # Begin Source File
 
+SOURCE=..\..\src\osgSim\LineOfSight.cpp
+# End Source File
+# Begin Source File
+
 SOURCE=..\..\src\osgSim\MultiSwitch.cpp
 # End Source File
 # Begin Source File
@@ -251,6 +259,10 @@ SOURCE=..\..\include\osgSim\Export
 # End Source File
 # Begin Source File
 
+SOURCE=..\..\include\osgSim\HeightAboveTerrain
+# End Source File
+# Begin Source File
+
 SOURCE=..\..\Include\osgSim\Impostor
 # End Source File
 # Begin Source File
@@ -283,6 +295,10 @@ SOURCE=..\..\include\osgSim\LightPointSystem
 # End Source File
 # Begin Source File
 
+SOURCE=..\..\include\osgSim\LineOfSight
+# End Source File
+# Begin Source File
+
 SOURCE=..\..\include\osgSim\MultiSwitch
 # End Source File
 # Begin Source File
diff --git a/examples/osgintersection/GNUmakefile b/examples/osgintersection/GNUmakefile
index f02d536f7..dd2c59628 100644
--- a/examples/osgintersection/GNUmakefile
+++ b/examples/osgintersection/GNUmakefile
@@ -4,7 +4,7 @@ include $(TOPDIR)/Make/makedefs
 CXXFILES =\
 	osgintersection.cpp\
 
-LIBS     += -losgText -losgGA -losgDB -losgUtil -losg $(GL_LIBS) $(X_LIBS) $(OTHER_LIBS) 
+LIBS     += -losgText -losgSim -losgGA -losgDB -losgUtil -losg $(GL_LIBS) $(X_LIBS) $(OTHER_LIBS) 
 
 INSTFILES = \
 	$(CXXFILES)\
diff --git a/examples/osgintersection/osgintersection.cpp b/examples/osgintersection/osgintersection.cpp
index 0f0f20a04..db226fdbc 100644
--- a/examples/osgintersection/osgintersection.cpp
+++ b/examples/osgintersection/osgintersection.cpp
@@ -8,6 +8,8 @@
 
 #include <osgUtil/IntersectionVisitor>
 
+#include <osgSim/LineOfSight>
+
 #include <iostream>
 
 struct MyReadCallback : public osgUtil::IntersectionVisitor::ReadCallback
@@ -45,8 +47,62 @@ int main(int argc, char **argv)
 
 
     bool useIntersectorGroup = true;
+    bool useLineOfSight = true;
     
-    if (useIntersectorGroup)
+    if (useLineOfSight)
+    {
+        osg::Timer_t startTick = osg::Timer::instance()->tick();
+    
+        osg::Vec3d start = bs.center() + osg::Vec3d(0.0,bs.radius(),0.0);
+        osg::Vec3d end = bs.center();// - osg::Vec3d(0.0, bs.radius(),0.0);
+        osg::Vec3d deltaRow( 0.0, 0.0, bs.radius()*0.01);
+        osg::Vec3d deltaColumn( bs.radius()*0.01, 0.0, 0.0);
+        unsigned int numRows = 50;
+        unsigned int numColumns = 50;
+
+        osgSim::LineOfSight los;
+
+        for(unsigned int r=0; r<numRows; ++r)
+        {
+            for(unsigned int c=0; c<numColumns; ++c)
+            {
+                osg::Vec3d s = start + deltaColumn * double(c) + deltaRow * double(r);
+                osg::Vec3d e = end + deltaColumn * double(c) + deltaRow * double(r);
+                los.addLOS(s,e);
+            }
+        }
+
+
+        los.computeIntersections(root.get());
+        
+        osg::Timer_t endTick = osg::Timer::instance()->tick();
+
+        std::cout<<"Completed in "<<osg::Timer::instance()->delta_s(startTick,endTick)<<std::endl;
+
+#if 0
+        for(unsigned int i=0; i<los.getNumLOS(); i++)
+        {
+            const osgSim::LineOfSight::Intersections& intersections = los.getIntersections(i);
+            for(osgSim::LineOfSight::Intersections::const_iterator itr = intersections.begin();
+                itr != intersections.end();
+                ++itr)
+            {
+                 std::cout<<"  point "<<*itr<<std::endl;
+            }
+        }
+#endif
+
+        // now do a second traversal to test performance of cache.
+        startTick = osg::Timer::instance()->tick();
+
+        los.computeIntersections(root.get());
+        
+        endTick = osg::Timer::instance()->tick();
+
+        std::cout<<"Completed in "<<osg::Timer::instance()->delta_s(startTick,endTick)<<std::endl;
+
+    }
+    else if (useIntersectorGroup)
     {
         osg::Timer_t startTick = osg::Timer::instance()->tick();
     
diff --git a/include/osgUtil/IntersectionVisitor b/include/osgUtil/IntersectionVisitor
index 5cc50fe35..2bd23a134 100644
--- a/include/osgUtil/IntersectionVisitor
+++ b/include/osgUtil/IntersectionVisitor
@@ -15,6 +15,7 @@
 #define OSGUTIL_INTERSECTIONVISITOR 1
 
 #include <osg/NodeVisitor>
+#include <osg/Drawable>
 #include <osgUtil/Export>
 
 #include <list>
diff --git a/src/osgSim/GNUmakefile b/src/osgSim/GNUmakefile
index 545b3cd26..47f44ed2c 100644
--- a/src/osgSim/GNUmakefile
+++ b/src/osgSim/GNUmakefile
@@ -13,6 +13,8 @@ CXXFILES = \
 	LightPointDrawable.cpp\
 	LightPointSpriteDrawable.cpp\
 	LightPointNode.cpp\
+	LineOfSight.cpp\
+	HeightAboveTerrain.cpp\
 	MultiSwitch.cpp\
 	OverlayNode.cpp\
 	OpenFlightOptimizer.cpp\
diff --git a/src/osgUtil/IntersectionVisitor.cpp b/src/osgUtil/IntersectionVisitor.cpp
index 5434d7be2..6e15c52e2 100644
--- a/src/osgUtil/IntersectionVisitor.cpp
+++ b/src/osgUtil/IntersectionVisitor.cpp
@@ -1,3 +1,16 @@
+/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield 
+ *
+ * This library is open source and may be redistributed and/or modified under  
+ * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
+ * (at your option) any later version.  The full license is in LICENSE file
+ * included with this distribution, and on the openscenegraph.org website.
+ * 
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
+ * OpenSceneGraph Public License for more details.
+*/
+
 
 #include <osgUtil/IntersectionVisitor>