INTEGRATED TRACKING SYSTEM AND FRAMEWORK FOR CONTEXT AWARE ENGINEERING APPLICATIONS

Transcription

1 INTEGRATED TRACKING SYSTEM AND FRAMEWORK FOR CONTEXT AWARE ENGINEERING APPLICATIONS By Manu Akula and Prof. Vineet R. Kamat UMCEE Report No Civil and Environmental Engineering Department UNIVERSITY OF MICHIGAN Ann Arbor, MI May 2010 Copyright 2010 by Manu Akula and Prof. Vineet R. Kamat

2 ABSTRACT Evolving technologies such as context aware computing offer significant potential of improving decision making tasks in several engineering applications by providing support for tedious and time consuming activities associated with timely and accurate access to needed information. Bi-directional flow of information relevant to the spatial context of a mobile user requires continuous and accurate tracking of the user s position and orientation. The tracking technology used cannot be dependent on installed infrastructure because it is not possible to install such infrastructure in every building. Additionally, a disaster may cause partial or complete damage to the installed infrastructure itself. The Global Positioning System (GPS) is a convenient option because it is independent on pre-installed infrastructure; however it fails when the line of sight to the satellites is obstructed. To overcome this problem, this report presents research that investigated the development and effectiveness of a ubiquitous location tracking system based on the integration of Real Time Kinematic Global Positioning System (RTK-GPS) and Personal Dead Reckoning (PDR) technologies for dynamic user position tracking. The designed GPS-PDR switching algorithms, along with experimental results documenting system effectiveness based on path complexity, length and duration are described. The report also describes a software and hardware framework developed for implementing complex ubiquitous context-aware computing applications in civil engineering. ii

3 ACKNOWLEDGMENTS I would like to express my sincere appreciation to Professors Vineet R. Kamat and Johann Borenstein and my colleagues Suyang Dong and Adam Borrell for their assistance in the preparation of this report, whose familiarity with various location tracking technologies were helpful during the programming and experimental phase of this research undertaking. I would like to thank my family for their valuable support through my academic career. I would also like to thank my friends for their assistance and support, for always being there to back me up with words of encouragement and constructive criticism. Manu Akula May, 2010 iii

4 TABLE OF CONTENTS 1 INTRODUCTION IMPORTANCE OF RESEARCH RESEARCH OBJECTIVE 2 2 REAL TIME KINEMATIC GLOBAL POSITIONING SYSTEM 4 3 PREVIOUS WORK ON INDOOR TRACKING TECHNOLOGIES 7 4 OVERVIEW OF NON-GPS NAVIGATION WITH PERSONAL DEAD-RECKONING SYSTEM INTRODUCTION TO PDR PDR HARDWARE PDR DATA PACKETS 17 5 INTEGRATED TRACKING SYSTEM INTEGRATED TRACKING SYSTEM COMPONENTS INTEGRATED TRACKING SYSTEM ALGORITHM Principle behind the Integration Algorithm Switching in the Integration Algorithm GPS Corrections to PDR Position VISUALIZATION OF THE INTEGRATED TRACKING SYSTEM 22 6 VALIDATION EXPERIMENTS INTRODUCTION TO THE VALIDATION EXPERIMENTS VALIDATION EXPERIMENTS RESULTS CONCLUSIONS FROM VALIDATION EXPERIMENTS Advantages of Using an Integrated Tracking System 28 7 GENERIC PLATFORM FOR UBIQUITOUS CONTEXT-AWARE APPLICATIONS IN CIVIL ENGINEERING OVERVIEW OF LOCATION TRACKING OVERVIEW OF ORIENTATION TRACKING Tracking System Hardware The Visual Frustum and the Line of Sight 32 iv

5 7.3 MOBILE USER AVATAR The Mobile User's Body Avatar The Mobile User's Head Avatar THE ENVIRONMENT IN CONTEXT THE MOBILE USER'S CONTEXTUAL VIEWS The Bird's Eye Point of View The First Person Point of View 36 8 CONCLUSIONS AND FURTHER STUDY CONCLUSIONS FROM WORK DONE FURTHER WORK 39 REFERENCES 44 v

6 LIST OF FIGURES Fig 1 Trimble AgGPS RTK Base 900 tracking system used in this research 5 Fig 2 Indoor GPS transmitter & receiver 7 Fig3 Comparative summary of indoor positioning technologies 8 Fig 4 Approach to RFID based indoor localization 9 Fig 5 Fig 6 Dolphin transmitter and receiver used by Hazas and Hopper in developing broadband ultrasonic location systems 10 System architecture of low cost location tracking system based on wireless technologies 11 Fig 7 Indoor positioning systems according to accuracy and range 12 Fig 8 The small sized nimu developed at the University of Michigan strapped onto a mobile user s shoe 16 Fig 9 Definition of the body coordinate system of the PDR 17 Fig 10 The Integrated Tracking System Arrangement 18 Fig 11 Flowchart for the integration algorithm pseudo code 21 Fig 12 ITS algorithm during switch from outdoors to indoors 22 Fig 13 Interface of Widely Integrated Simulation Environment 22 Fig 14 Architecture of Widely Integrated Simulation Environment (WISE) 23 Fig 15 The concept of jump in the ITS during a typical walk experiment 24 Fig 16 ITS accuracy and range when operated outdoors and indoors 29 Fig 17 Roll, Pitch and Yaw angles defined for airplanes and a human s view 30 Fig 18 TCM5 magnetic orientation tracker chip mounted on a helmet 31 Fig 19 Mobile user s line of sight and viewing frustum 32 Fig 20 The mobile user avatar with the viewing frustum attached to the head and computational assumptions to capture avatar s body s motion 34 vi

7 Fig 21 Fig 22 Fig 23 Fig 24 Four samples among several different environments loaded as geometric files on the framework for context aware engineering applications 35 Bird s Eye Point of View of the mobile user and the Construction Lab in the G. G. Brown building, University of Michigan, Ann Arbor 36 The First Person View of the mobile user while observing the Construction Lab in the G.G. Brown building, University of Michigan, Ann Arbor 37 Three types of non-straight motion better captured by the PDR with heuristic drift correction 40 Fig 25 Architecture of manual position correction in ITS 41 vii

8 LIST OF TABLES Table 1 Jumps in ITS co-ordinates for short and simple walks 26 Table 2 Jumps in ITS co-ordinates for short and complex walks 26 Table 3 Jumps in ITS co-ordinates for longer walks 27 Table 4 Jumps in ITS co-ordinates for the six parts of the sustainability test 27 Table 5 Average Jumps in ITS co-ordinates for different walks 28 viii

9 1. INTRODUCTION 1.1 IMPORTANCE OF RESEARCH Context aware computing is defined as the use of environmental characteristics such as a user s location, time, identity, profile and activity that is relevant to the current context. [3] Context aware computing can thus potentially enable mobile users (e.g. construction inspectors, firefighters) to leverage knowledge about various context parameters to ensure that they get highly specific information, pertinent to the decisions at hand. The relevance for context awareness for mobile users has been demonstrated in several applications by Aziz et al. [1] The concept of context-aware information delivery centers around the creation of a user centered mobile dynamic indoor and outdoor work environment, which has the ability to deliver relevant information to on-site mobile users by intelligent interpretation of their characteristics in space and time so that they can take more informed decisions. [12] Context awareness is of great value for civil engineering inspectors, emergency responders, security and military personnel. For example, tracking civil engineers during post disaster assessments, or while conducting bridge inspection reports, can allow bi-directional flow of streamlined information and thereby improve the efficiency of the decision making processes. Bridge inspections are currently documented manually but will be done virtually in the near future. If a bridge inspector looking at a particular element of the structure wants to report data regarding the status of the structure, s/he can pin the report in the form of a suitable data file (.doc,.txt,.jpeg,.avi, etc.) to the element in context in a virtual model of the bridge under consideration. If the inspector is looking at a particular element of the structure and wants to read all the data corresponding to the element, the inspector can tap into a database and retrieve the necessary information depending on his/her context. 1

10 Context-aware applications can be used in providing support to complex, tedious and time consuming tasks. Civil engineers, fire fighters, military personnel and a host of other professionals stand to benefit from context-aware applications as it makes bidirectional flow of information more efficient and relevant based on a mobile user s context. 1.2 RESEARCH OBJECTIVE To implement context aware support applications we must be able to track a user s position and orientation continuously and accurately. The Global Positioning System (GPS) tracks users accurately and continuously in an environment where there is a direct line of sight to the satellites. However, when there is no direct line of sight, the system fails. In recent times, cars have been using GPS to navigate. However, when a car enters a long tunnel, the GPS signal is lost and cannot track the location of the car on its own. To overcome this deficiency, some cars have a GPS tracking system that is complemented by an Inertial Navigation Unit (INU) mounted on the wheels. The INU tracks the motion of the car via. its orientation and the number of rotations of the car s wheel whenever the GPS signal is lost. This ensures that the vehicle is tracked continuously even in a GPS deficient environment. GPS can also be used to track a moving person in an environment where there is a direct line of sight with the satellites to acquire a position via GPS. The word outdoors is used to describe such an environment in this report unless specifically mentioned otherwise. The word indoors is used to describe all environment where GPS tracking is not possible due to a lack of communication with the satellites. There are several indoor tracking technologies available that help in tracking a mobile user continuously and accurately in a GPS denied environment as described in detail in chapter 3. However, most of these tracking 2

11 technologies are dependent on pre-installed infrastructure and pre-calibrated data. The research described in this report is focused on developing an Integrated Tracking System that ubiquitously tracks a mobile user s position both indoors and outdoors independent of installed infrastructure. This is done by integrating GPS with a suitably chosen indoor tracking technology to complement each other. In general, on a construction site and other dynamically changing environment where the mobile user shifts his/her location from indoors to outdoors and vice versa without prior knowledge of whether the user is within the range of particular tracking technology, it is of utmost importance that the Integrated Tracking System seemingly translates automatically from an outdoor tracking technology to an indoor tracking technology without any prompting from the mobile user. Another objective of the research is to develop the prototype of a basic platform for visualizing a mobile user s context in his/her environment in which the user is changing his/her position and orientation. A dynamic user-viewpoint tracking scheme has been designed and implemented in which mobile users spatial context is defined not only by their position (i.e. location), but also by their three-dimensional head orientation (i.e. line of sight), thereby significantly increasing accuracy in the identification of a user s spatial context than is possible by tracking position alone. Based on this framework, a prototype application was developed using GPS, Personal Dead Reckoning (PDR) and magnetic orientation tracking devices to track a user s dynamic viewpoint in different environments. The framework developed in this research can be used as a base for developing several context-aware applications in civil engineering. 3

12 2. REAL TIME KINEMATIC GLOBAL POSITIONING SYSTEM The Global Positioning System (GPS) is a space-based global navigation satellite system that provides reliable location information in all weather at all times and anywhere on earth where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver. Location tracking applications based on GPS are available at several levels based on the accuracy required by the users. At the personal level, there are several GPS tracking devices available in the market. Hand held GPS receivers, with replaceable batteries that can run them for several hours, are suitable for tracking users during hiking, bicycle touring and other activities far from an electric power source. In recent years, one of the most popular GPS based tracking application has been the commercially available Personal Navigation Assistant - a portable electronic product which combines a positioning capability (through GPS) and navigation functions. Several different versions of the Personal Navigation Assistant have been developed by companies like Garmin, TomTom, Navman and Magellan. These systems use GPS at a personal level and have relatively low accuracy, typically within the range of two to four meters. As mentioned in the previous chapters some high end Personal Navigation Assistants have the capability to track the vehicles even when GPS is unavailable. Such situations occur typically when a vehicle enters a tunnel or an urban canyon where there is no direct line of sight to the GPS satellites. This is accomplished by integrating the GPS positioning system with an Inertial Navigation Unit that tracks the vehicle in a GPS denied environment. The idea behind the Integrated Tracking System described in this 4

13 report is based on similar principles. However, the GPS units used by the Personal Navigation Assistants are typically of lower accuracy than what is desired by contextaware engineering applications. Fig 1: Trimble AgGPS RTK Base 900 tracking system used in this research The GPS system used in this research as a component of the Integrated Tracking System is a survey level Trimble AgGPS RTK Base 900 system incorporated with Real Time Kinematic technology. Real Time Kinematic (RTK) satellite navigation is a technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the GPS where a single reference station provides the realtime corrections, providing up to centimeter-level accuracy. The typical nominal accuracy for these RTK-GPS systems is 1 centimeter horizontally and 2 centimeters vertically. The RTK-GPS has the ability to track a mobile user continuously and accurately as long as the mobile user is outdoors. However, when the user moves into a GPS denied indoor environment, we must rely on an indoor tracking technology that is to be incorporated in the Integrated Tracking System to complement the RTK-GPS. Several such indoor tracking technologies, described in the next chapter, were looked at during the course of this research. The Personal Dead Reckoning System described in 5

14 chapter 4 was found to be the most suitable system to be incorporated in the Integrated tracking System due to reasons described in the next two chapters. 6

15 3. PREVIOUS WORK ON INDOOR TRACKING TECHNOLOGIES In recent years, the need for indoor localization has been rapidly expanding in many fields and currently offers significant potential on construction sites in particular. However, unlike outdoor areas, the indoor environment imposes different challenges on location discovery due to the dense multipath effect and building material dependent propagation effect. There are many potential technologies and techniques that have been suggested to offer the same functionality as a GPS indoors, such as Wireless Local Area Networks (WLAN), Ultra-Wide Band (UWB) and Indoor GPS. By tagging users with appropriate receivers/tags and deploying a number of nodes (access points, receivers, transmitters, etc.) at fixed positions indoors, the location of tagged users can conceptually be determined and continuously tracked by fingerprinting and triangulation. Fig 2: Indoor GPS transmitter & receiver [6] A detailed comparison of the WLAN, UWB and Indoor GPS systems has also been done in a recent study by Kamat and Khoury. [6] The research studied and compared three different wireless technologies (WLAN, UWB and Indoor GPS), that can be used 7

16 for tracking mobile users on indoor construction sites. In order to evaluate and compare the technical features of these technologies and their applicability in a context-aware information delivery framework, several experiments were conducted at the University of Michigan, Disaster City (Texas A&M University), and NIST. Based on the experiments, it was found that the decision on using one technology over another should be based on important technical criteria (e.g. calibration, line of sight, etc.) in addition to other logistic issues such as availability, the prevailing legal situation (e.g. permitted bandwidth), and the associated implementation costs. However, based on the circumstances expected in the intended deployment environment (i.e. indoor construction sites), the Indoor GPS positioning technology was found to offer the most promise due to the low level of uncertainty in the reported user position (1 to 2 cm) compared to that of WLAN (1.5 to 2 m) and UWB (10 to 50 cm). [6] Fig 3: Comparative summary of indoor positioning technologies [6] RFID also has the capability to locate users in an indoor environment. In most of the research studies on using radio frequency for indoor localization, typically some readers/receivers are placed at fixed locations and a tag/transmitter is attached to a mobile object or a person. A converse approach has also been pursued by Pradhan, Ergen and Akinci. [11] Instead of multiple readers, multiple tags were placed at fixed locations and a reader is carried by the person, who was to be located in the building 8

17 with respect to the tags. The study developed an approach to assess the capability of RFID in helping to locate a user using RFID signal strength values and conducted experiments to test the approach under real operating conditions. The research identified a set of requirements for guidance (directional reliability, time invariance, and spatial accuracy and precision) and evaluated the requirements for RFID signal strength approach. The approach in this research (using one reader to locate a user) was found to be 93% accurate for 10.7 m of precision. [11] Fig 4: Approach to RFID based indoor localization [11] Ultrasonic location systems are a popular solution for the provision of indoor positioning data. Applications include enhanced routing for wireless networks, computer-aided navigation, and location-sensitive device behavior. However, using narrowband transducers in ultrasonic location systems result in several limitations. Hazas and Hopper [4] have developed and characterized ultrasonic indoor location systems that use broadband ultrasonic transmitter and receiver units. Their research dealing with the utilization of broadband and narrowband units to construct two positioning systems with 9

18 different architectures serves to highlight and affirm the concrete, practical benefits of broadband ultrasound for locating people and devices indoors. Hazas and Hopper [4] have demonstrated that ultrasonic indoor location systems based on broadband units have the potential for significantly higher performance in a number of aspects of system operation than their narrowband counterparts because broadband systems can utilize spread spectrum, multiple access techniques in their ranging signals. [4] Fig 5: Dolphin transmitter and receiver used by Hazas and Hopper in developing broadband ultrasonic location systems [4] Broadband ultrasonic systems have been shown to have a number of advantages over their narrowband counterparts. The performance enhancements for location systems using broadband ultrasound include enhanced performance in noise robustness, increased update rates, low latency positioning (this means location updates for multiple people and devices can be nearly simultaneous) and enhanced identification encoding (transmitter signals can be uniquely identified at the receiver since broadband signals have a much greater capacity to carry information). [4] 10

19 Mautz [7] describes an automatic, low-cost system that exploits wireless communication technology to enable continuous tracking of the location of devices, and consequently users carrying those devices, in all environments (indoors and outdoors). The research describes the development of a wireless sensor network that involves system design, digital signal processing, protocol development, extraction of ranges and localization including a high level strategy for the positioning function based on an ad-hoc geodetic network positioning method which is evaluated on issues of accuracy, quality and reliability of the node positions. It was demonstrated that it is possible to achieve a position deviation that is of the size of the ranging error. [7] Fig 6: System architecture of low cost location tracking system based on wireless technologies [7] Mautz [7] indicates that tracking of devices and users needs to have full coverage in different environments indoors as well as outdoors. Consequently, the system should 11

20 not be denoted as an indoor positioning system in order to take into account geodetic applications to monitoring larger natural or man-made structures. The required navigation performance depends on the type of environment. To accommodate these diverse accuracy demands, the system needs to be based on a precise geodetic network positioning function as well as a coarse positioning mode comparable to mobile phone localization schemes. [7] Fig 7: Indoor positioning systems according to accuracy and range [8] Kohoutek, Mautz and Donaubauer [13] consider a novel indoor positioning method that is currently under development at the Eidgenössische Technische Hochschule (ETH) 12

21 Zurich. The method relies on a digital spatio-semantic interior building model CityGML and a Range Imaging sensor. In contrast to common indoor positioning approaches, the procedure presented here does not require local physical reference infrastructure, such as WLAN hot spots or reference markers. However, this method depends on image sensing and cannot be relied upon especially a dynamically changing environment, for instance when a building is partially or fully damaged, we cannot expect to use an image sensing localization system to be reliable. Mautz [8] compares several indoor positioning systems including AGNSS & high sensitivity receivers, pseudolites using GNSS signals, laser tracking, igps and ultrasonic systems. [8] The main drawback of the aforementioned indoor tracking technologies is their dependency on pre-installed infrastructure and pre-calibration for fingerprinting. Also, most technologies are environment (outdoors and indoors) specific. Such dependency makes them unreliable in a dynamic environment because we cannot expect every building to have pre-installed infrastructure and pre-calibration done for fingerprinting. Also, in a dynamically changing environment, where a mobile user moves from outdoors to indoors and vice versa changing his/her environment, it is obviously beneficial to have a comprehensive location tracking system that can be used reliably irrespective of his/her environment. Moreover, the pre-installed infrastructure may be partially or fully damaged in case of a post disaster assessment scenario. It is therefore of utmost importance that we do not rely on such indoor tracking technologies and there is a need to use indoor tracking technologies that are independent on pre-installed infrastructure and pre-calibration techniques. To overcome this we recommend the use of Personal Dead Reckoning (PDR) tracking systems for indoor tracking. PDR systems are based on Inertial Navigation and are independent of pre-installed infrastructure. Although less accurate than WLAN, UWB and Indoor GPS, they provide us with sufficient accuracy 13

22 that degrades gracefully with extreme modes of legged locomotion. Chapter 4 of this report describes the PDR system used in this research in greater detail. 14

23 4. OVERVIEW OF NON-GPS NAVIGATION WITH PERSONAL DEAD-RECKONING SYSTEM 4.1 INTRODUCTION TO PDR The PDR system used in this research is the Personal Odometry System (POS) developed by Ojeda and Borenstein [9] at the University of Michigan, Ann Arbor. The POS uses data from the accelerometers and gyroscopes in the Inertial Measurement Unit (IMU) sensor attached to the user s boots. From this data the POS computes the complete trajectory of the boot during each step. The POS offers the following features: o Linear Displacement: This is the most important and most basic function of the system the measurement of distance traveled, but without measuring the direction. This function works like the odometer of a car, which also does not measure the direction of travel. The POS performs this function with an error of about 2% of distance traveled; regardless of duration or distance. The POS is also indifferent to the stride length and pace, as well as to the gait. There is also no need for calibration or fitting the system to the walking pattern of a specific user. The accuracy of the PDR system, however, degrades gracefully with extreme modes of legged locomotion, such as running, sideways motion, walking backwards, jumping, and climbing. [10] o Position Estimation: This capability includes odometry as well as the measurement of direction. Position estimation allows the system to determine the subject s actual location in terms of x, y, and z coordinates, relative to a known starting location. The measurement of direction is based on the use of 15

24 gyroscopes, which are known to have drift, just as accelerometers do. However, the correction method that is applied to the accelerometers in not effective for gyros. Therefore, the system is currently susceptible to the accumulation of heading errors over time. The system also measures vertical position, but less accurately so. [10] The main drawback of the PDR system is the accumulated error that grows with the distance travelled by the mobile user. To overcome this, we have developed algorithms that integrated PDR positioning systems with GPS systems that will correct the drifting error accumulated over time. 4.2 PDR HARDWARE The current prototype uses a high quality small sized light nano IMU (nimu in short) made by MemSense. The nimu is strapped to the side of the mobile user s foot, as shown in Fig. 4. Fig 8: The small sized nimu developed at the University of Michigan strapped onto a mobile user s shoe 16

25 The IMU is connected to a tablet-style laptop computer through an RS-422 communication port. The IMU is powered using a small external 7.8-Volt Lithium Polymer battery, making the whole system portable. The computer runs the Linux operating system patched with a real-time extension and our algorithm runs in real-time. [9] 4.3 PDR DATA PACKETS The PDR system transmits data in the form of packets. Each packet comprises of ten fields including position X, Y, Z and heading. The starting point of the walk serves as the origin of the PDR system. The system s design requires that the user walks the first 8 steps in a straight line. The PDR system internally calibrates this line as its Y-axis. The Z-axis is axis that is vertically upwards from the origin. Using this right hand co-ordinate system, the PDR reports the mobile user s position in terms of X, Y and Z coordinates relative to the user s starting position. Fig 9: Definition of the body coordinate system of the PDR In this research and the experiments that are a part of it, the user has always taken the first eight steps, required by the PDR system for calibration, aligned with the North direction thus aligning the Y-axis of the PDR system towards North. 17

26 5. INTEGRATED TRACKING SYSTEM 5.1 INTEGRATED TRACKING SYSTEM COMPONENTS The Integrated Tracking System (ITS) consists of components of both RTK-GPS and PDR systems. The subject wears a backpack with the GPS receiver in it. The IMU of the PDR system is strapped to the subject s foot. The computer in the PDR system is hooked into the subject s pocket. Fig 10: The Integrated Tracking System Arrangement A magnetic tracker that determines the subject s orientation is attached to the hard hat worn by the subject. The GPS, PDR and tracker systems are connected to the serial ports of a small laptop containing the ITS software. 18

27 5.2 INTEGRATED TRACKING SYSTEM ALGORITHM Principle behind the Integration Algorithm The ITS records the mobile user s current location as dictated by the RTK-GPS and the PDR separately. However, the coordinate system used by the PDR is different from the World Geodetic System 84 (WGS 84) latitude, longitude, altitude coordinate system used by the RTK-GPS. To resolve this issue, the ITS uses Vincenty s Forward Pass Algorithm for WGS 84 to convert the user s location from a local X, Y, Z coordinate system to a location on the WGS 84 - latitude, longitude, altitude coordinate system. The accuracy of RTK-GPS (3 to 5 centimetres) is much higher than the accuracy of the PDR. Also, the accuracy of the PDR decreases with the distance travelled by the mobile user. As a result the position of the user as dictated by the RTK-GPS is almost always inevitably more accurate than the position dictated by the PDR. The principle behind determining the ITS co-ordinates is that RTK-GPS co-ordinates, if available, always take precedence over the PDR co-ordinates Switching in the Integration Algorithm When the mobile user enters a GPS denied environment such as indoor structures, urban canyons, etc. the ITS no longer receives the mobile user s position as dictated by the RTK-GPS system. When the ITS loses connectivity with the RTK-GPS system, the ITS ensures that the position of the mobile user is the position as dictated by the PDR system adjusted for drift correction. These adjustments are described in detail in Section The ITS continues to locate the mobile user s position as dictated by the PDR for the entire duration that the user is in the GPS denied environment. As soon as the mobile user steps out of the GPS denied environment and receives a signal from the RTK-GPS 19

28 system, the ITS switches back and the ITS mobile user s location is dictated once again by the RTK-GPS system. The integration algorithm of the ITS seamlessly switches between the RTK-GPS and PDR systems when required and thus provides the most reliable location of the mobile user continuously and accurately in both indoor and outdoor environments. The accuracy of the PDR degrades gracefully with the distance travelled by the mobile user and this is reflected in the accuracy of the ITS when the user is in a GPS denied environment for longer durations GPS Corrections to PDR Position The main drawback of the PDR system is that it accumulates drift error over time. This drift error is accumulated irrespective of whether the GPS is available or not. The PDR position is corrected to the RTK-GPS position by the ITS as long as the RTK-GPS signal is available. The correction is equal to the different in position between the RTK- GPS and PDR positions. In effect, as long as the RTK-GPS signal is available the corrected PDR position is the same as the RTK-GPS position. This correction would eliminate all drift accumulated in the PDR and therefore the ITS as long as the RTK- GPS is available. Once the user loses contact with the RTK-GPS signal, the correction applied is equal to the difference in the last known RTK-GPS location and its corresponding PDR location. From that point onwards, till the RTK-GPS is recovered, the same correction is applied to the PDR location. This in effect means that the only drift that will be accumulated by the PDR would be the drift accumulated during the mobile user s walk in a GPS denied environment. The constant correction being applied by the ITS to the PDR location in GPS denied environment makes sure that it nullifies the effect of drift accumulated in the user s walk till the very last time the user has entered the particular GPS denied environment. Once the user steps out of the GPS denied environment, the ITS regains the RTK-GPS signal, however, this may not 20

29 happen immediately as the user steps into a location with available GPS positioning because it takes some time to establish the connection with the RTK-GPS. Fig 11: Flowchart for the integration algorithm pseudo code Once the GPS is regained, the correction is adjusted and the PDR drift becomes zero as the adjusted PDR location would once again become equal to the RTK-GPS location due to the new corrections. This updated correction manifests itself as a jump in the location of the position of the user from the ITS at that point in time when the ITS switches taking command from the newly available RTK-GPS instead of the PDR position. The concept of the integration algorithm is described as a flowchart in Fig

30 When the accuracy of the ITS falls below desired levels, the mobile user can step outside, recover the RTK-GPS signal, correct his/her PDR location using the RTK-GPS signal and step back inside the GPS denied environment and continue navigation. Fig 12: ITS algorithm during switch from outdoors to indoors 5.3 VISUALIZATION OF THE INTEGRATED TRACKING SYSTEM Fig 13: Interface of Widely Integrated Simulation Environment 22

31 The ITS is visualized on Widely Integrated Simulation Environment (WISE) that was developed at the University of Michigan by Suyang Dong and Vineet R. Kamat. The WISE interface displays the location of the user in a Google Earth environment. The mobile user s path is recorded by the ITS along with a record which component, RTK- GPS or PDR, dictates the particular portion of the path as a KML file in real time. This KML is replayed on the server side that is read by a HTTP request. The path is displayed as an animation in the Google Earth API. On the right hand side of the GUI, there is a counter that displays the position in terms of latitude, longitude, altitude of the user s current position as displayed in the post process animation. WISE has features that will allow the user to view the simulation at 2, 4 and 8 times the natural rate. It also has options to pause and retrieve the position of the user at any point on the path. Fig 14: Architecture of Widely Integrated Simulation Environment (WISE) 23

32 6. VALIDATION EXPERIMENTS 6.1 INTRODUCTION TO THE VALIDATION EXPERIMENTS The experimental results obtained with the ITS described in the foregoing section. These results focus on three different types of experiments (1) short and simple walks, (2) short and complex walks and (3) longer walks. Fig 15: The concept of jump in the ITS during a typical walk experiment Short and simple walks Relatively simple walks having duration between 3 to 5 minutes (indoors) are classified as short walks. These walks involved few turns and almost no abrupt disturbances in motion. 24

33 Short and complex walks Relatively complex walks having duration between 3 to 5 minutes (indoors) are classified as short and complex walks. These walks involved relatively more turns, abrupt disturbances in motion, climbing and sideward motion. Longer walks Relatively complex walks having duration over 5 minutes (indoors) are classified as longer walks. These involved relatively more turns, abrupt disturbances in motion, climbing and sideward motion. To test the sustainability of the ITS we conducted a very long walk (over 30 minutes). The walk involved a lot of turns, abrupt disturbances in motion, climbing and sideward motion in order to simulate a mobile user s natural motion in a complex environment. The walk was divided into 6 parts; 3 parts were of a short duration, less than 5 minutes indoors, and rest were longer. At the end of each part, the user walked out of the building, recovered the RTK-GPS correcting the error in the ITS and continued his/her walk into the building. 6.2 VALIDATION EXPERIMENTS RESULTS Short and simple walks Table 1 summaries the jumps in the user s position (ITS co-ordinates) when the user steps out of the building as GPS is recovered. The jump is the difference in the last dominant corrected PDR co-ordinates and the first recovered GPS co-ordinates. This is equal to the accumulated error of the PDR during the time spent by the user inside the building (i.e. when) PDR corrections were not being updated instantaneously using the RTK-GPS). 25

34 Walk 1 Walk 2 Walk 3 Walk 4 Last dominant PDR(Lat) Last dominant PDR(Long) Recovered GPS (Lat) Recovered GPS (Long) Jump (meter) Table 1: Jumps in ITS co-ordinates for short and simple walks Short and complex walks Table 2 summarizes the jumps in the user s ITS position co-ordinates when the GPS is recovered. Walk 1 Walk 2 Walk 3 Walk 4 Last dominant PDR(Lat) Last dominant PDR(Long) Recovered GPS (Lat) Recovered GPS (Long) Jump (meter) Table 2: Jumps in ITS co-ordinates for short and complex walks Longer walks Table 3 summarizes the jumps in the user s ITS position co-ordinates when GPS is recovered. 26

35 Walk 1 Walk 2 Walk 3 Walk 4 Last dominant PDR(Lat) Last dominant PDR(Long) Recovered GPS (Lat) Recovered GPS (Long) Jump (meter) Table 3: Jumps in ITS co-ordinates for longer walks Sustainability test walks Table 4 summarizes the walk used for testing ITS sustainability. Duration (Min:sec) Last dominant PDR (Lat) Last dominant PDR (Long) Last dominant GPS (Lat) Last dominant GPS (Long) Jump (meters) Part 1 4: Part 2 4: Part 3 4: Part 4 7: Part 5 8: Part 6 8: Table 4: Jumps in ITS co-ordinates for the six parts of the sustainability test 27

36 6.3 CONCLUSIONS FROM VALIDATION EXPERIMENTS As tested to date, the ITS is very accurate for tracking smooth walks. The accuracy of the ITS, reflects that of the PDR and degrades gracefully with both path complexity and time spent indoors. Once the accumulated drift in the ITS starts to overshoot the satisfactory level the user needs to step outdoors and recover the GPS signal to reset the corrections. Depending on the degree of accuracy required by the context-aware application, the required frequency of corrections can be determined. The average jump in the ITS co-ordinates when the GPS is recovered increases with the time spent indoors. This is expected because the corrections to the PDR are not being updated instantaneously due to RTK-GPS being unavailable. Table 9 summarizes the experimental results. Type of walk Average Duration Indoors Average jump Short and simple walks 3 minutes 45 seconds 1.4 meters Short and complex walks 3 minutes 45 seconds 2.6 meters Longer walks 6 minutes 15 seconds 3 meters Table 5: Average Jumps in ITS co-ordinates for different walks Advantages of Using an Integrated Tracking System The Integrated Tracking System (ITS) described in this work is truly independent of environment. The ITS can adapt and translate seamlessly from an outdoor environment to an indoor environment and vice versa. Also, it can be implemented in a dynamically changing environment as it doesn t depend on any image reorganization. The ITS is independent of pre-installed infrastructure and has absolutely no requirements for pre- 28

37 calibration or fingerprinting process common in indoor localization technologies. This would reduce tremendous amount of time and effort and would eliminate the need for data storage. The ITS can be implemented in a post disaster scenario, where traditional localization systems may fail due to partial or full damage to the preinstalled infrastructure. The ITS developed in this research is a truly robust, reliable system that determines a user s location continuously with a high degree of accuracy. The ITS is a light weight mobile, flexible and easy to use tracking device that can be used to help locate mobile users in dynamically changing environments. The ITS can be tremendously useful for inspectors, emergency response crews, military personnel, etc. One specific application is described in the following chapter. Fig 16: ITS accuracy and range when operated outdoors (red) and indoors (green) 29

38 7. GENERIC PLATFORM FOR UBIQUITOUS CONTEXT- AWARE APPLICATIONS IN CIVIL ENGINEERING We have been developing a generic platform for ubiquitous context aware applications with some inherent elementary features. The platform can be modified in the future and can be tailored to suit the specific context aware application required. 7.1 OVERVIEW OF LOCATION TRACKING The ITS described in the previous chapters dictates the mobile user s location, in terms of latitude (x), longitude (y) and altitude (z), to the platform. However, these three measurements are not enough to define a user s context. 7.2 OVERVIEW OF ORIENTATION TRACKING As noted in the previous section, in order to understand a mobile user s fully qualified spatial context, another parameter other than position is required. This parameter is the user s head s orientation in three dimensions. The direction in which the mobile user is looking is defined by three angles roll, pitch and yaw. The roll, pitch and yaw angles are typically used to define the direction of orientation of an airplane. Fig 17: Roll, Pitch and Yaw angles defined for airplanes and a human s view [5] 30

39 Yaw represents the rotation in the horizontal plane, pitch is the rotation in the vertical plane parallel to the forward direction, and roll is the rotation in the vertical plane perpendicular to the forward direction Tracking System Hardware The orientation tracker is a TCM5 magnetic orientation tracker. It includes a built-in compass, and employs solid-state magnetic field sensors which measure compass heading through a full 360 degrees of rotation. The tracker employs proprietary hard and soft iron correction algorithms to calibrate out magnetic anomalies for repeatable, high resolution measurement in challenging environments. The tracker is enclosed in an aluminum container and is placed at the lowest point on the user s helmet, directly above the forehead. This ensures that the orientation of the tracker is as close to the line of sight of the user as possible. Fig 18: TCM5 magnetic orientation tracker chip (left) mounted on a helmet (right) The ITS measure s a user s position as longitude (x), latitude (y) and altitude (z) while the magnetic tracker measures the orientation of the user s head, and consequently the line of sight, in the form of roll, pitch and yaw. These six measurements fully define the user s context at any point of time. 31

40 7.2.2 The Visual Frustum and the Line Of Sight The line of sight in itself is not a complete representation of the region of space visible to the mobile user. The region of real space visible to a mobile computing user can be conceptually thought of to be similar to an avatar s viewpoint in a computer graphics application or virtual reality world. In a computer graphics world (e.g., visual simulation), the region of visible virtual space is called the viewing frustum or view frustum, and is typically shaped as a frustum of a rectangular pyramid. [11] Based on the concept of the viewing frustum, and the six measurements that define the user s context (position and orientation) we mathematically derived the formulation for the region of space visible to a mobile computing user. Objects closer to the user than the near plane or beyond the far plane are assumed to be out of sight and context. Typically, the near plane is chosen close to the user s viewpoint and the far plane is placed infinitely far away so all objects within the frustum are considered to be of interest regardless of their distance from the user. Fig 19: Mobile user s line of sight and viewing frustum 32

41 The platform has a provision for adjusting the near and far plane distances at any point in the simulation. A large value for the far plane distance would typically represent the situation where the far plane is at infinity. The platform can be modified by using ray casting algorithms to identify objects that fall within the viewing frustum and therefore are in the mobile user s context. 7.3 MOBILE USER AVATAR The platform has a mobile user s avatar in the virtual world to represent the mobile user and his/her motion. To capture the complexity of human motion, the avatar is divided into two components the avatar head and the avatar body. There is an option provided to scale the avatar of the user based on the height of the mobile user using the system The Mobile User s Body Avatar The mobile user s body is modeled as an ac3d CAD model. The body s position is determined by the ITS s coordinates in the form of latitude (x), longitude (y) and altitude (z). As described previously, the height of the body s avatar can be scaled based on the height of the mobile user. The user s body orientation can be captured by assuming that the body is oriented in the direction of the user s motion. If the previous position of the user can be indicated by the vector P1 and the current position vector of the user can be indicated by P2, then the direction of orientation of the user s body is defined by the difference in the position vectors P2 and P1, in the direction of motion (i.e., P1 to P2). 33

42 Fig 20: The mobile user avatar with the viewing frustum attached to the head (left) and computational assumptions to capture avatar s body s motion (right) The shortcoming of this approximation done in order to simplify the body s motion is that we cannot capture sideward or backward motion. However, this minor shortcoming helps simplify the process of capturing the motion of the user in the simulation The Mobile User s Head Avatar The user s head position is determined by the ITS s position. However, it is set at a fixed distance above the user s body s avatar. This fixed distance is a function of the user s height. The orientation of the user s head is determined by the orientation of the tracker. The viewing frustum is attached to the head s avatar, just between the eyes in the virtual environment. 34

43 7.4 THE ENVIRONMENT IN CONTEXT The framework allows for the environment of the mobile user to be replicated in the virtual world by loading the appropriate geometric file. The platform has the ability to load any file format for which there is a plugin in OpenSceneGraph This includes the following geometric file formats: 3dc, 3ds, flt, geo, iv, ive, lwo, md2, obj, osg and ac3d. It also includes the following image file formats: bmp, gif, jpeg, rgb, tga, tif. Fig 21: Four samples among several different environments loaded as geometric files on the framework for context aware engineering applications 7.5 THE MOBILE USER S CONTEXTUAL VIEWS The platform provides two different views of the virtual environment 1) a third person point of view and 2) a first person point of view. 35

44 7.5.1 The Bird s Eye Point of View One of the cameras provided by the platform is a 3 rd person or a bird s eye point of view of the mobile user in his/her virtual environment. The camera follows the mobile user throughout the scene at a fixed distance behind the mobile user. The camera always looks slightly down towards the user. Fig 22: Bird s Eye Point of View of the mobile user and the Construction Lab in the G. G. Brown building, University of Michigan, Ann Arbor The First Person Point of View The platform also provides a second camera that shows the mobile user s context i.e., the mobile user s first person view. This view is set so that it is always bounded by the 36

45 visual frustum. The two cameras when viewed side by side on the screen can be used as a reference guide by the mobile user in performing the task. Fig 23: The First Person View of the mobile user while observing the Construction Lab in the G.G. Brown building, University of Michigan, Ann Arbor The basic platform described in this chapter can be tailored to meet specific requirements of the context aware application at hand. One such application is in developing a context aware platform for the cyber-enabled wireless monitoring systems for the protection of deteriorating national infrastructure systems. The objective of this task is to investigate methods to facilitate efficient interaction between human inspectors in the field and the pervasive sensor network that will monitor the state of a bridge or supporting structures. The specific goal of the research is to design and 37