Added support for reading and writing Sphere, Box, Cone, Cylinder and Grid shapes.

src/osg/ShapeDrawable.cpp

@@ -734,6 +734,8 @@ void ComputeBoundShapeVisitor::apply(const ConvexHull& hull)
 void ComputeBoundShapeVisitor::apply(const HeightField& field)
 {
 
+
+
     float zMin=FLT_MAX;
     float zMax=-FLT_MAX;
 
@@ -747,6 +749,12 @@ void ComputeBoundShapeVisitor::apply(const HeightField& field)
 	}
     }
 
+    if (zMin>zMax)
+    {
+        // no valid entries so don't reset the bounding box
+        return;
+    }
+
 	    
     if (field.zeroRotation())
     {