GPS World, July 2015

Algorithms Methods INNOVATION critical navigation applications but is largely neglected in current vision navigation research The concept of integrity particularly for navigation systems refers to the level of trust that can be placed in a navigation system in terms of detecting gross errors and divergences Many navigation applications have adopted the use of protection levels which are real time navigation system outputs that bound the navigation errors to the required probability of integrity risk For the case of vertical navigation the vertical navigation system error NSE is bounded by the real time vertical protection level VPL and as the long as the VPL is below the vertical alert limit VAL the system can continue its operation Loss of integrity is defned by the case when the NSE VAL without an alert or in other words when NSE VAL and VPL VAL One of the richest sources of information for how integrity can be handled for precision relative navigation systems can be found with the Local Area Augmentation System LAAS which focused on providing integrity under fault free and single ground reference receiver failure conditions LAAS employs several quality monitors such as receiver autonomous integrity monitoring RAIM Much of the vision aided navigation research to date has focused more on system and algorithmic robustness rather than quantitative and verifiable integrity particularly for feature based processing One approach has introduced the concept of regional bounding for feature correspondence between time sequenced image frames including some featureunique criteria that can provide some protection from feature correspondence errors Although this approach does yield some robustness for the algorithms no quantitative integrity characterization was developed Another approach introduced a truly quantitative integrity monitor for failures in the mapping of features to pixels particularly in the presence of a bias This approach predicts the largest possible position error in the presence of one such bias due to feature mismatch using a GPS RAIM type approach The current state of research addressing integrity for vision navigation using an image rendering or template matching approach is even less mature In fact we have not identifed any previous integrity specifc work for image rendering vision navigation The research presented in this article generalizes the concept of integrity in terms of operating and alerting regions Applications that use navigation systems generally have objective operating regions that require a certain navigation performance whether this be around a glide slope a formation fight position or even a fight path clearance Navigation integrity becomes critical because large divergences from these operating regions without an alert can become safety risks The alert limit is simply the instantiation of this concept It is the threshold or measure of how much undetected divergence from the operating region can be tolerated without inducing unacceptably large safety risks The remaining sections of this article will describe the development of a rigorous and quantitative vision aided Image correspondence Perturbation loop Initial state estimation Sensor image 3 D object model State perturbation 2 D object projection Template database Navigation estimation FIGURE 1 Image rendering relative navigation approach 55 Forward meters 0 Right meters Correspondence value 40 45 50 60 65 10 5 5 20 15 10 05 0 10 109 FIGURE 2 GRD based image correspondence illustration as a function of 2 D relative navigation state Detection rule H1 H0 P MD P FA Image correspondence value H1 PDF H0 PDF PDF p x FIGURE 3 Graphical illustration of detection performance integrity monitor for precision relative navigation systems First an introduction to relative navigation using image rendering will be covered in order to describe the fundamental vision navigation approach This will be followed by a detailed derivation of the proposed vision aided integrity monitor and simulation based performance results Using Image Rendering The basis of our research is that vision aided techniques specifcally image rendering can be used to construct a highperformance integrity monitor for precision relative navigation systems Image rendering approaches and or template matching have been used extensively in vision applications such as machine vision medical image registration object detection and pose estimation and recently as a precision navigation system www gpsworld com July 2015 GPS World 45