This paper describes the concepts and technique behind the Automatic Vehicle Location (AVL) and Vessel Tracking System (VTS) developed by HNIT LTD, and ALDIS LTD. in Iceland. The system are based upon standard GPS technology and Esri's GIS systems, ArcInfo and ArcView2. The paper describes the different communication methods that are used to monitor the movements of "dynamic objects" like cars or vessels and display them in a "real-time" GIS system. It describes also the new features in ArcInfo and ArcView2 to communicate with other applications through the InterApplication Communication (IAC) functions, and how the AVL and VTS system modules are integrated on the Enterprise Network. An example of AVL and VTS systems are described in the paper and also a prototype system running in Reykjavik and the currently available functions in the system and future implementations.
The integration of Geographic Information Systems (GIS) and GNSS (Global Navigation Satellite system, GPS and GLONASS) has created new and exciting possibilities in the field of information technology and remote observation. This integration allows fast, accurate and dynamic updates of geographic information and an easy-to-use interface to a very complex set of data. The recent introduction of GNSS technology has opened up possibilities to track and monitor movements of any kind of vehicles on land, ships on sea and aircraft in the air. This is done by combining the navigation technology with digital communications and microcomputer technologies. By this, it is for example possible to measure the position and velocity of a vehicle and transmit this information to a central monitoring station. These kind of systems are generally called Automatic Vehicle Location system (AVL), Vessel Tracking System (VTS) and Automatic Dependent Surveillance (ADS) for aviation.
HNIT LTD. and ALDIS LTD. of Iceland, two Icelandic companies that have many years of experience in the use of GIS systems and Navigational systems, have jointly developed and constructed an AVL and VTS systems that accomplishes this, and much more! The systems are based on state-of-the-art desktop GIS system (Arcview2 from Esri Inc.), standard GPS receivers, communication hardware, and software developed by Hnit and Aldis Ltd. A Relational Database Management System can also be integrated into the system. The system runs on UNIX or Windows Servers.
The Automatic Vehicle Location system allows the user to monitor and track the movements and precise location of cars equipped with GPS. Cars can for example be equipped with a DGPS 6-channel Differential GPS Sensor. This should give 3-10 m positioning accuracy of the vehicles within a city. The velocity of the moving cars can be measured within the accuracy of 1 Km/h. Single GPS receivers without the differential corrections give less accuracy and Positional errors over 100 m can be expected.
The GNSS requires that a line of sight to at least three satellites is maintained for positioning. By the use of multi-channel GNSS receivers this can be fulfilled for most urban areas. However, where houses block a great part of the hemisphere, this condition will not be fulfilled at all times. In tunnels, satellite positioning is not possible.
The communications link between the central monitoring station and the vehicles can be of various types. The most common methods are probably VHF/UHF radio link, Mobile telephones with both voice and data communication and Inmarsat Standard C satellite communications.
For urban use, VHF or UHF communications are the most cost effective solution. The AVL system developed by HNIT LTD. and ALDIS LTD. uses standard voice VHF transceivers for transmitting the digital information. The modulation used is called MSK or Minimum Shift Keying and the bit rate of the current system running in Reykjavik is 1200 b/s. Currently, development work at ALDIS LTD. is bringing the bit rate up to 4800 b/s or even 9600 b/s, still using 25 kHz wide communications channels.
It must be noted that by nature, VHF and UHF communications require a line of sight between the communicating parties. However, experience has shown that communications are often possible in spite of buildings or other objects obstructing the line of sight path. For best results it is necessary to use repeaters that cover those parts of a city that the central communications station can not cover. It is also important to place the communications stations on high locations within a city.
The vehicle is equipped with a multi-channel GNSS receiver, that utilises the GNSS satellites to compute the position. The navigation output of this receiver is fed to a microcomputer that stores the information and prepares the data to be transmitted via the VHF/UHF transceiver. If general data transmission capability is required, the addition of a keyboard and a display is required. Also, a printer onboard the automobile can be highly advantageous.
The central monitoring station controls all communications within the system. To facilitate this, polling is used as the communications protocol. The central monitoring station can either call individual vehicles or establish group calls. By group calls, better efficiency of the communications channel is achieved.
The central monitoring station maintains track of all vehicles within the system. The overview is provided by a geographical information system (GIS) running on the station's main computer system. The AVL system developed by HNIT ltd. and ALDIS uses ArcView2 as a geographical information system. ArcView interacts with the AVL GPS Server program that communicates with the vehicles and gets their positions. ArcView and the AVL GPS Server communicate through the Inter Application Communication functions (RPC/DDE calls) in ArcView.
All positioning information of the fleet of vehicles can be viewed graphically in the Geographic Information part of the system. The system has also the ability to collect the data from the vehicle for later playback or for analysis. One can mark all streets that a chosen vehicle has travelled in a given time and use the information for planning of later trips. The system can also alert the user when a vehicle is coming near some area of interest and perform some analysis like where is the nearest police car located to some place. The system can therefore be used both for viewing car locations and more complex analysis and decision making using the possibilities of the GIS system.
The system can be a front end to an external vehicle database that is accessed by pointing on a vehicle icon on the screen thus retrieving information on the vehicle from a database since SQL connections and connections to external databases is implemented in ArcView2. In addition to the GIS, many other applications may run on the central computer system. A database of all vehicle movements can be maintained, a connection to other databases residing on other computer systems is possible. The system can also administer external relational databases (RDBMS) which can store both text and image information. In the RDBMS, various administrative tasks can be performed, such as report writing and general information gathering. Access to this information can be controlled to avoid access from unauthorised users. The Positional GPS data can be coded and can only be decoded by the AVL system and is therefore locked from unauthorised use.
HNIT LTD. has recently released an application based upon ArcView2 "Emergency Rescue System" for fire departments. The application is implemented in close cooperation with the Fire Department in Reykjavik and GEODATA AS. in Norway. The initial goal of the application was to have a "mobile" system out in the field were the firemen in charge could have an digital overview of the building(s) on fire and have access to additional information like hazardous material and "attack plans" (pre planned). Monitoring of fire trucks and ambulances has now been seen as a valuable "add-on" to the system and VHF communications could be used to transmit data between fire trucks and between headquarters and fire trucks/ambulances. By using this technique the headquarters can send for example "location information" to the computers that are running the ArcView applications out in the fire trucks and they can automatically zoom into the actual area so when the fire crew enters the truck the environment is already set and the can immediately start to process the data for the building on fire while the truck is still driving to the specified address.
ALDIS LTD. has developed and installed a prototype system for the Icelandic Live Saving Organisation who has been responsible for the position reporting system for the Icelandic fishing fleet since 1968. In this reporting system every vessel has to report its position by voice every twelve hours as well as entering or leaving harbour. Since 1983 the System Engineering Laboratory of the University of Iceland has been involved in the design of an automatic VTS system for all Icelandic vessels and the goal of the system is to be able to get a position from each vessel within the Icelandic 200 nautical mile economic zone, at least every 15 minutes. It has also been a goal to be able to transmit user defined data between ship and shore as a "value added" service. The design approach has been to use Loran-C or GNSS (GPS/GLONASS) systems for positioning and use VHF datalink for ship to shore communication for smaller vessels and Inmarsat Standard C for vessels that go out of the VHF range. ALDIS LTD. has been responsible for the development of the prototype system since 1990. The Icelandic government made a decision 1994 to install VTS and to have all Icelandic vessels equipped with such system before the end of 1999. In 1994 ALDIS LTD. and HNIT LTD. integrated the VTS system and ArcView so that the additional function available in the GIS system could also be accessible for the proposed VTS system and would not have to be implemented specially.
In general the VTS systems have two main purposes. The first is to be able to monitor the position of a fleet of ships from ashore and to have tools to both transmit messages to the ships and receive messages from them. The second purpose is to provide accurate navigational equipment on board the ship and to offer the possibility of an electronic Captains logbook.
The system approach taken by ALDIS LTD. and HNIT LTD. is to use only commercially available hardware. This implies that the availability of components is not at risk. For the communications of larger vessels that go out of the VHF reach, Inmarsat Standard-C was chosen and the Global Positioning System, GPS as a navigational aid. Inmarsat Standard-C gives almost a world-wide service, only the polar areas of approximately north 80 Deg N and south 80 Deg S are not covered. GPS gives a world-wide service. The positioning accuracy of the vessels is within 100 m.
Through the system design, effort has been made to have the system as reliable as possible. Because of this constraint, both the land based as well as ship based part of the system are completely self sufficient in the sense that their only requirement is AC Power, either 220 VAC or 120 VAC. The ship borne part does not rely on any other equipment on board the ship, and even the AC power is taken through an Uninteruptable Power Supply, UPS, which makes it possible to have the ship equipment operational for about one hour without any external power. The same goes for the land based part of the system, it only requires AC power, it does not rely on access to for example local telephone lines. Similar to the ship equipment, the AC power is taken through a UPS unit which is mainly to filter out disturbances on the AC system. The UPS is also able to keep the system operational for short periods of AC outages.
On the ship there are four main units, GPS receiver, Inmarsat Standard-C terminal, Personal Computer (PC) with printer and a power regulating system. Following is a description of each unit.
GPS Unit: The GPS receiver gives, on a world wide basis, the position, speed and heading of the ship. The accuracy of the position is within 100 meters, but built in the GPS unit is a Differential corrections receiver, which locks on to differential corrections transmitted by ILEA when it is available. When the unit is within the coverage of such a transmission the position accuracy is within 5 meters. Attached to the GPS unit is a display where the position and movement of the ship can be viewed on a map which shows the coastline. Many different maps are available from the manufacturer, but the user can also generate his own. The GPS unit can record the movements of the ship into a memory. Later these recorded tracks can be displayed along with the current movement of the ship. Apart from these features, the GPS unit has all standard features.
Inmarsat Standard-C Terminal: The Standard-C terminal gives almost a world wide coverage for data communications. Only the polar areas are not covered. The system uses four geostationary satellites and one of a number of Land Earth Stations. The Galaxy Inmarsat-C/GPS terminal from TRIMBLE has a built in GPS receiver and can be programmed to send position, speed and heading of the ship on a periodic basis, completely independent of all other units onboard the ship. The terminal is normally used in data mode where data from external computer onboard the ship is transmitted ashore or to other ships, and received data from shore or ships is sent to the onboard computer.
Personal Computer (PC): On the PC there are programs that communicate with the standard C terminal, both for transmitting and receiving data. Through the PC the ship can send messages and reports both to shore and also to other ships. The PC will run special programs which make entry of catch data and related information easy. Also the PC will be able to run all standard software, such as DOS, WINDOWS, WORD, EXCEL and the Captains Electronic Logbook (CEL).
Power Regulation: The UPS (Uninteruptable Power Supply) takes in AC power, either 220 VAC 50 Hz or 120 VAC 60 Hz and stabilises it so that the PC and Standard-C terminal can be run off it. The UPS has also batteries which can keep the equipment operative for one hour in case of power outage. The GPS operates on 24 VDC through a voltage converter that is run off the UPS.
The land based equipment can be composed of the following units. UNIX or Windows Workstations make up the backbone of the computing power. They run ArcView and GPS Server software for receiving and displaying the global positions and RDBMS software for recording, keeping and updating the reports from individual vessels. The Workstations can be interconnected on a Local Area Network (LAN) along with Personal Computers (PC) on an Enterprise Network. The purpose of the additional PCs is threefold:
For communications with the vessels, an Inmarsat Standard-C terminal is used, almost identical to the one in the ships. With this system set-up, there are no requirements for use of local facilities other than AC power. It is suggested to use two sets of Standard-C transceivers. The reason is to provide redundancy. To minimise possible effects of disturbances on the AC power lines, all power is filtered through UPS before being applied to the system.
The new IAC functions in ArcView2 and ArcInfo 7.0 have opened many possibilities to integrate different technology. GIS and GPS have been available for many years and combined in a single integrated application environment they form a very strong alliance. High performance state-of-the-art systems can be implemented using "standard" commercial hardware and software like the Esri's GIS and GPS systems from TRIMBLE and other GPS vendors. Many AVL and VTS systems are using their own geographical information systems and often use raster maps as background and display the positonal information on top of those. This has of course its limitations and we see it as a better solution to be able to use ArcInfo and ArcView for the GIS part and get all the extra functions that are already there instead of having to implement it all. In some cases the use of a commercial GIS could be difficult because of strict rules in the response time of the system (specially in ADS, aviation).