addressed Dave's comments

src/rviz/default_plugin/covariance_visual.cpp

@@ -302,7 +302,7 @@ void CovarianceVisual::setCovariance( const geometry_msgs::PoseWithCovariance& p
   // store orientation in Ogre structure
   Ogre::Quaternion ori;
   if (!normalizeQuaternion(pose.pose.orientation, ori))
-    ROS_WARN("invalid quaternion (zero length)");
+    ROS_WARN("Invalid quaternion (zero length)");
 
   // Set the orientation of the fixed node. Since this node is attached to the root node, it's orientation will be the
   // inverse of pose's orientation.

src/rviz/default_plugin/interactive_markers/interactive_marker.cpp

@@ -121,7 +121,7 @@ bool InteractiveMarker::processMessage( const visualization_msgs::InteractiveMar
       message.pose.position.z );
 
   if (!normalizeQuaternion(message.pose.orientation, orientation_))
-     ROS_WARN("invalid quaternion (zero length)");
+     ROS_WARN("Invalid quaternion (zero length)");
 
   pose_changed_ =false;
   time_since_last_feedback_ = 0;

src/rviz/default_plugin/pose_array_display.cpp

@@ -67,7 +67,7 @@ namespace
   {
     Ogre::Quaternion q;
     if (!normalizeQuaternion(quaternion, q))
-      ROS_WARN("invalid quaternion (zero length)");
+      ROS_WARN("Invalid quaternion (zero length)");
     return q;
   }
 }

src/rviz/validate_quaternions.h

@@ -70,6 +70,7 @@ inline double quaternionNorm2(double w, double x, double y, double z)
 
 inline bool validateQuaternion(double w, double x, double y, double z)
 {
+  // use same threshold as in tf
   return std::abs(quaternionNorm2(w, x, y, z) - 1.0) < 10e-3;
 }