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Mr. Kirk Burnell
P.Eng; Hemisphere GPS
4110 9th Street SE, Calgary, Alberta, Canada
kburnell@hemispheregps.com
Ms. Olga Flerkevitch
EIT, Hemisphere GPS
4110 9th Street SE, Calgary, Alberta, Canada
oflerkevitch@hemispheregps.com
Value of SBAS to Positioning in Emerging Applications
Mr. Kirk Burnell
P.Eng; Hemisphere GPS
4110 9th Street SE, Calgary, Alberta, Canada
kburnell@hemispheregps.com
Ms. Olga Flerkevitch
EIT, Hemisphere GPS
4110 9th Street SE, Calgary, Alberta, Canada
oflerkevitch@hemispheregps.com
Abstract
The geospatial industry often relies on Global Navigation Satellite Systems (GNSS) to provide position information. While such satellite systems on their own are accurate for some applications, many techniques of augmenting their accuracy exist. The simplest systems for users to employ are Satellite-Based Augmentation Systems (SBAS). Project operators can maximize the value of their work by improving the positioning accuracy of their data. This extends the useful life of the data, reducing the need for re-surveying. Also, by avoiding complex field techniques, project operators can reduce operation expenses. Some applications where this has proved successful are surveying, mapping and Geographic Information Systems (GIS), utilities, natural resources, public and private land information systems, precision agriculture, aviation and marine navigation, railway management, and port handling. This paper explores how improving position accuracy through SBAS adds value to several of these applications.
Introduction
There are several levels of GNSS accuracy that can be achieved; the difference is in equipment used and the techniques. Since Global Positioning System (GPS) and GNSS receivers vary tremendously in features and price, it is important to establish the level of accuracy required for a given application. For the purpose of this paper GNSS receivers for civil use are roughly subdivided into three categories; although additional levels of classification are possible, three categories are sufficient for the analysis. Category I includes geodetic grade receivers with millimeter accuracy and fast position update rates. Category II comprises of receivers with SBAS and precision multipath resistant antennas providing precision grade accuracy. Category III includes receivers which may have SBAS capabilities, but are offered in mass consumer markets at low prices. Depending on the application, accuracy requirements, update rates and budget, one can chose which receiver is most suitable.
Common Levels of Accuracy Commercially Available
Category I
High accuracy receivers offer survey-grade accuracy levels that are commonly utilized in traditional land surveying. Receivers in this category employ Real Time Kinematic (RTK) data services, high level multipath resistant external antennas, and high update rates to achieve centimeter and millimeter accuracy. Equipment in this category can be used in various applications but is limited by its selling price. The high price defines the market for Category I, and therefore limiting it to such applications as high precisions surveying.
Category II
Category II receivers are the most widely used when high positioning accuracy is required. These receivers achieve sub-meter accuracy with the assistance of SBAS corrections. Systems use techniques similar to Category I receivers with less sophisticated technology and often utilize phase measurements to smooth solutions. The price is approximately one fifth to one eighth of the price of a Category I system, greatly broadening the applications. Applications for such receivers can range from GIS to surveying. Some systems can be upgraded to provide accuracy like Category I systems for an additional cost. This upgradeability is not seen in the other Categories.
Category III
Category III refers to handheld receivers and OEM boards or chip sets that may be integrated into handheld recreational positioning devices or Personal Navigation Devices (PND’s). All of these use code measurements for the real-time estimation of the position, as well as filter algorithms for smoothing. The price ranges between one tenth and one quarter of the price of a Category II receiver, which is reflected in the positioning accuracy. The accuracy of these low cost receivers is restricted to several meters.
Comparing Categories
As the popularity of GPS increases, more applications rely on receivers to provide continuous, reliable data. Typical problems for receivers are caused by signal blockage and multipath. When the receiver is under heavy tree canopy or in an urban canyon or tunnel, the GPS signal is blocked, causing lapses in received data. Category I and II receivers employ various measurement techniques to provide precise positioning information. Low cost Category III receivers must rely on other approaches to provide solutions. This could include matching positions to digital maps or using dead reckoning sensors, such as odometers, compasses, and gyroscopes.1 When employing these methods, the position solution relies on external data, such as the accuracy of the map or the gyroscope, further degrading the accuracy. These methods, however, do require additional hardware, increasing the cost of the unit.
SBAS is typically used in Category II and III receivers to achieve higher accuracy at no additional cost to the user in areas that are covered by SBAS networks. By utilizing this service, Category II receivers are able to achieve sub-meter accuracy, but Category III receivers still struggle to achieve three to five meters.
An additional concern in selecting a receiver is the position update rate. In many applications an update rate of 1Hz is sufficient and is available in all categories of receivers. If, however, a receiver is used in kinematic positioning a higher update rate is often required for continuous position data. Higher update rates are only available in Category I and II receivers, making them the desired choice in kinematic applications. In addition, the types of data available in a Category III receiver are limited. This limits the ability to provide quality analysis on data, making it difficult to confirm that the system is providing suitable accuracy.
When using GPS it is also important to take satellite coverage into account. At various times of day and at various locations on the Earth’s surface, the number of satellites and the length of time they are above the observer’s horizon will vary. If the position cannot be calculated due to poor satellite coverage, Category I and II receivers will stop outputting solutions, while Category III receivers will strive to provide a solution at the expense of accuracy. This behavior degrades the quality and reliability of data that is already lacking in accuracy.
One area of apprehension when purchasing a GPS receiver is the possible need for a higher accuracy system in the future. As areas of GPS applications grow, the level of accuracy required from a receiver may rise. Category III receivers are not capable of improved performance and would require purchasing new receivers in a higher accuracy bracket. However, some receivers in Category II are capable of operating at higher accuracy modes, providing centimeter level accuracy for various applications. Certain upgrades are required such as new firmware and radio modems. The modified system will not have the full performance of a Category I system – startup times will be slower – but the cost of the receiver and the necessary upgrades will nonetheless be significantly lower than that of a Category I system (figure 1).
Figure 1: Categories of GPS receivers
Opportunities Utilizing SBAS-Improved Positioning
Surveying, Mapping and GIS
One of the most appropriate uses for GPS is in Surveying. The highest accuracy receivers available, Category I, are in use in this field. They are the most expensive receivers and are also complex to operate, as a sound knowledge of surveying is assumed to be possessed by the user. Price and complexity of use are the two most common things limiting the use of receivers in surveying.2
Mapping and GIS use a different class of receiver, typically from Category II or III. These receivers tend to be easier to use with few or no cables and fewer controls for the receiver. This makes it much easier to operate and the typical user does not need much knowledge and training in GPS. While the low price of Category III receivers is attractive, the products themselves are intended more for recreational users, such as car navigation or handheld receivers designed for adventurers. While they can store positions, they do not integrate well with computer software –they are not designed as daily use data collectors. As well, when operating under SBAS, a Category III receiver may reach 5m position accuracy, while a Category II receiver can achieve 0.3 meters. This accuracy level is suitable for many applications that might otherwise require a surveyor.
Utilities and Natural Resources
When adding data to a GIS, the quality of the data ultimately determines the useful life of the database. For a first GIS, even ten meter accuracy can be useful as compared to no GIS. But eventually ten meter accuracy will not be sufficient, and another costly resurvey of the features, assets or resources will be required. By using high accuracy Category II equipment from the beginning, the data can be collected properly the first time. Using easy to operate integrated receivers will also improve the efficiency of data collection, minimizing survey costs.
Figure 2: Managing natural resources has a variety of positioning accuracy requirements
Figure 3: Costs can be easily recovered through efficiency improvements in many areas of the marine market
To collect accurate data, some differential source should be used. SBAS enhanced receivers provide corrected positions without added complexity in their design. As well, the coverage area of an SBAS system is ideal for utility companies, where their assets are located over wide and often remote areas. Natural resources are also often in remote locations with little infrastructure and again SBAS signals in those regions simplifies data collection (figure 2).
Public and Private Land Information Systems
Managing a nation’s growth is an immense task. So many data indicators exist and with a limited budget it is essential to invest public money where it will have the greatest impact. Using a GIS within the government to attribute economic data by location is an effective way to manage growth.
Governments should strive to create land information systems to increase their ability to gather, interpret, and act on information, to detect trends, and to permit better decision-making.3
When relying on survey-grade (Category I) answers for land information systems, which is customary for governments to consult with their survey departments, it is often extremely costly to extend that level of accuracy. It also takes a long time to obtain the data, delaying the ability for decision makers to utilize it from within the land information system.3 Allowing precision positioning (Category II) instead of survey grade significantly reduces cost and gets the job done much quicker, often by a labor force that is less costly than having the survey department provide answers.
Precision Agriculture
In emerging applications, agricultural exports show considerable, sustained growth. In India, for example, there has been a 68% increase in agricultural exports within the past four years, growing at a rate of over 16% year over year.4 With rising commodity prices, it becomes more economically viable to consider producing the exports with greater efficiency
The World Trade Organization (WTO) is encouraging producers to adopt modern agricultural production techniques and technologies. Suggested areas for modernization address:5
Aviation
From early on, the aviation community could see the benefits of using GPS for navigation. What was needed was a monitoring system that could also increase reliability. The result was SBAS networks. Although regional, SBAS coverage areas are very broad, allowing users from many industries and areas to take advantage of the free correction services. As a result, many companies produce aviation GPS receivers that are SBAS ready. As most aerial applications require aircraft to maintain separations of hundreds of meters for safety, Category III receivers are often more than capable of the job. However, there are applications where precision is still important, for tasks such as aerial crop dusting and fire fighting, and Category II systems are the answer.
Marine Navigation
In history, a strong economy required trading. Since much trading was done over seas and oceans, navigation has always been important to economic success. The same is true today. Using GPS in marine applications offers low cost navigation to all users by providing accurate position and speed information. Operators can save money by saving time and fuel.6 The improved efficiency benefits everyone with lower shipping and insurance costs as well as the environment (figure 3).
SBAS enhances safety on the water much like in the air. Category III receivers are affordable on the smallest of vessels, providing safety to users who otherwise could not afford solutions. When using SBAS the improved accuracy makes low cost Category II receivers suitable for many workboats, where precision matters. Applications range from sweeping and dredging to automated buoy positioning.6
Railway Management
Another cost effective means of transportation is by rail. While trains do not need satellites to navigate, there are still many advantages to using at least a Category II or III receiver for scheduling, collision avoidance, and maintenance.7 Scheduling generally does not require precise positioning but does require an integrated solution. Category II receivers typically offer easy integration at an attractive price. Collision avoidance requires sub-meter performance and high reliability to determine which tracks the trains are on, and what speed and direction they are going. This clearly requires SBAS enabled Category II receivers. Maintenance information about track conditions can be collected by trains equipped with GPS and other sensors to keep the tracks in proper repair.10 This also requires Category II SBAS receivers.
Some rail systems are part of other site facilities such as mines and port facilities. Using SBAS enhanced GPS in such places is just one important piece to achieving better efficiency and optimization for the entire operation.
Port Handling
Sea ports are the gateways into and out of countries. Goods travel by truck or train to the port where they are loaded onto boats. Thousands of containers pass through the port every day and it is surprisingly easy to misplace a container. GPS and GIS are used to track where every container is placed in the yard. This makes them easy to relocate when it is time to ship. When combined with other identification technologies like RFID or barcodes, smart port systems simplify on-site container storage, reduce container retrieval time, and reduce the time ships are in port.9 This improves port efficiency. Even after only a few months of operation, one port in China reported a cost reduction of 8%, and a 10% increase in productivity.6
Figure 4: Port facilities can be congested and have many signal obstructions
Even though a container is large, its position has to be known to 0.5 meters or better to prevent the lift cranes from driving down the wrong aisle to retrieve it. As well, there are many places in the port where there are obstructions to satellite visibility (figure 4). The receivers used have to recover from signal outages and settle to sub-meter accuracy within a very short time. Combined with the 0.5 meters accuracy requirement, Category II receivers are an obvious choice. Without SBAS, ports must setup their own base station and use radio links to each vehicle to receive corrections. With up to 300 vehicles in a large port, the additional equipment costs and complexity can be considerable.
Results and Discussion
Given the need to succeed through efficient, cost effective programs, emerging applications can benefit greatly by employing a variety of GPS technologies and techniques. The most significant gains can be realized when an SBAS correction service is available in the region. Many applications can take advantage of the cost savings available by not having to utilize alternate correction services and also easier learning curves with the simplified equipment. Most consumer priced GPS systems will see a small improvement in accuracy when SBAS is present, while high-end RTK survey systems will not benefit at all. The Category II products, (the precision positioning systems), will benefit the most. They will improve from two to three-meter accuracy up to 0.3-meter accuracy.
Having had the opportunity to work with many different GPS receivers, the authors note that the Crescent series of GPS receivers offered by Hemisphere GPS are capable of the precision positioning systems discussed in this paper. There are very few other systems offered by other manufacturers that can meet this accuracy. For a look at the different products available and their specifications, please visit the company’s website at http://www.hemispheregps.com.
References
The geospatial industry often relies on Global Navigation Satellite Systems (GNSS) to provide position information. While such satellite systems on their own are accurate for some applications, many techniques of augmenting their accuracy exist. The simplest systems for users to employ are Satellite-Based Augmentation Systems (SBAS). Project operators can maximize the value of their work by improving the positioning accuracy of their data. This extends the useful life of the data, reducing the need for re-surveying. Also, by avoiding complex field techniques, project operators can reduce operation expenses. Some applications where this has proved successful are surveying, mapping and Geographic Information Systems (GIS), utilities, natural resources, public and private land information systems, precision agriculture, aviation and marine navigation, railway management, and port handling. This paper explores how improving position accuracy through SBAS adds value to several of these applications.
Introduction
There are several levels of GNSS accuracy that can be achieved; the difference is in equipment used and the techniques. Since Global Positioning System (GPS) and GNSS receivers vary tremendously in features and price, it is important to establish the level of accuracy required for a given application. For the purpose of this paper GNSS receivers for civil use are roughly subdivided into three categories; although additional levels of classification are possible, three categories are sufficient for the analysis. Category I includes geodetic grade receivers with millimeter accuracy and fast position update rates. Category II comprises of receivers with SBAS and precision multipath resistant antennas providing precision grade accuracy. Category III includes receivers which may have SBAS capabilities, but are offered in mass consumer markets at low prices. Depending on the application, accuracy requirements, update rates and budget, one can chose which receiver is most suitable.
Common Levels of Accuracy Commercially Available
Category I
High accuracy receivers offer survey-grade accuracy levels that are commonly utilized in traditional land surveying. Receivers in this category employ Real Time Kinematic (RTK) data services, high level multipath resistant external antennas, and high update rates to achieve centimeter and millimeter accuracy. Equipment in this category can be used in various applications but is limited by its selling price. The high price defines the market for Category I, and therefore limiting it to such applications as high precisions surveying.
Category II
Category II receivers are the most widely used when high positioning accuracy is required. These receivers achieve sub-meter accuracy with the assistance of SBAS corrections. Systems use techniques similar to Category I receivers with less sophisticated technology and often utilize phase measurements to smooth solutions. The price is approximately one fifth to one eighth of the price of a Category I system, greatly broadening the applications. Applications for such receivers can range from GIS to surveying. Some systems can be upgraded to provide accuracy like Category I systems for an additional cost. This upgradeability is not seen in the other Categories.
Category III
Category III refers to handheld receivers and OEM boards or chip sets that may be integrated into handheld recreational positioning devices or Personal Navigation Devices (PND’s). All of these use code measurements for the real-time estimation of the position, as well as filter algorithms for smoothing. The price ranges between one tenth and one quarter of the price of a Category II receiver, which is reflected in the positioning accuracy. The accuracy of these low cost receivers is restricted to several meters.
Comparing Categories
As the popularity of GPS increases, more applications rely on receivers to provide continuous, reliable data. Typical problems for receivers are caused by signal blockage and multipath. When the receiver is under heavy tree canopy or in an urban canyon or tunnel, the GPS signal is blocked, causing lapses in received data. Category I and II receivers employ various measurement techniques to provide precise positioning information. Low cost Category III receivers must rely on other approaches to provide solutions. This could include matching positions to digital maps or using dead reckoning sensors, such as odometers, compasses, and gyroscopes.1 When employing these methods, the position solution relies on external data, such as the accuracy of the map or the gyroscope, further degrading the accuracy. These methods, however, do require additional hardware, increasing the cost of the unit.
SBAS is typically used in Category II and III receivers to achieve higher accuracy at no additional cost to the user in areas that are covered by SBAS networks. By utilizing this service, Category II receivers are able to achieve sub-meter accuracy, but Category III receivers still struggle to achieve three to five meters.
An additional concern in selecting a receiver is the position update rate. In many applications an update rate of 1Hz is sufficient and is available in all categories of receivers. If, however, a receiver is used in kinematic positioning a higher update rate is often required for continuous position data. Higher update rates are only available in Category I and II receivers, making them the desired choice in kinematic applications. In addition, the types of data available in a Category III receiver are limited. This limits the ability to provide quality analysis on data, making it difficult to confirm that the system is providing suitable accuracy.
When using GPS it is also important to take satellite coverage into account. At various times of day and at various locations on the Earth’s surface, the number of satellites and the length of time they are above the observer’s horizon will vary. If the position cannot be calculated due to poor satellite coverage, Category I and II receivers will stop outputting solutions, while Category III receivers will strive to provide a solution at the expense of accuracy. This behavior degrades the quality and reliability of data that is already lacking in accuracy.
One area of apprehension when purchasing a GPS receiver is the possible need for a higher accuracy system in the future. As areas of GPS applications grow, the level of accuracy required from a receiver may rise. Category III receivers are not capable of improved performance and would require purchasing new receivers in a higher accuracy bracket. However, some receivers in Category II are capable of operating at higher accuracy modes, providing centimeter level accuracy for various applications. Certain upgrades are required such as new firmware and radio modems. The modified system will not have the full performance of a Category I system – startup times will be slower – but the cost of the receiver and the necessary upgrades will nonetheless be significantly lower than that of a Category I system (figure 1).
Figure 1: Categories of GPS receivers
Opportunities Utilizing SBAS-Improved Positioning
Surveying, Mapping and GIS
One of the most appropriate uses for GPS is in Surveying. The highest accuracy receivers available, Category I, are in use in this field. They are the most expensive receivers and are also complex to operate, as a sound knowledge of surveying is assumed to be possessed by the user. Price and complexity of use are the two most common things limiting the use of receivers in surveying.2
Mapping and GIS use a different class of receiver, typically from Category II or III. These receivers tend to be easier to use with few or no cables and fewer controls for the receiver. This makes it much easier to operate and the typical user does not need much knowledge and training in GPS. While the low price of Category III receivers is attractive, the products themselves are intended more for recreational users, such as car navigation or handheld receivers designed for adventurers. While they can store positions, they do not integrate well with computer software –they are not designed as daily use data collectors. As well, when operating under SBAS, a Category III receiver may reach 5m position accuracy, while a Category II receiver can achieve 0.3 meters. This accuracy level is suitable for many applications that might otherwise require a surveyor.
Utilities and Natural Resources
When adding data to a GIS, the quality of the data ultimately determines the useful life of the database. For a first GIS, even ten meter accuracy can be useful as compared to no GIS. But eventually ten meter accuracy will not be sufficient, and another costly resurvey of the features, assets or resources will be required. By using high accuracy Category II equipment from the beginning, the data can be collected properly the first time. Using easy to operate integrated receivers will also improve the efficiency of data collection, minimizing survey costs.
Figure 2: Managing natural resources has a variety of positioning accuracy requirements
Figure 3: Costs can be easily recovered through efficiency improvements in many areas of the marine market
To collect accurate data, some differential source should be used. SBAS enhanced receivers provide corrected positions without added complexity in their design. As well, the coverage area of an SBAS system is ideal for utility companies, where their assets are located over wide and often remote areas. Natural resources are also often in remote locations with little infrastructure and again SBAS signals in those regions simplifies data collection (figure 2).
Public and Private Land Information Systems
Managing a nation’s growth is an immense task. So many data indicators exist and with a limited budget it is essential to invest public money where it will have the greatest impact. Using a GIS within the government to attribute economic data by location is an effective way to manage growth.
Governments should strive to create land information systems to increase their ability to gather, interpret, and act on information, to detect trends, and to permit better decision-making.3
When relying on survey-grade (Category I) answers for land information systems, which is customary for governments to consult with their survey departments, it is often extremely costly to extend that level of accuracy. It also takes a long time to obtain the data, delaying the ability for decision makers to utilize it from within the land information system.3 Allowing precision positioning (Category II) instead of survey grade significantly reduces cost and gets the job done much quicker, often by a labor force that is less costly than having the survey department provide answers.
Precision Agriculture
In emerging applications, agricultural exports show considerable, sustained growth. In India, for example, there has been a 68% increase in agricultural exports within the past four years, growing at a rate of over 16% year over year.4 With rising commodity prices, it becomes more economically viable to consider producing the exports with greater efficiency
The World Trade Organization (WTO) is encouraging producers to adopt modern agricultural production techniques and technologies. Suggested areas for modernization address:5
- eco-friendly land water usage
- promote the effective utilization of chemical, biological and mechanical inputs to increase productivity and conserve resources
- modernize commercial agriculture to facilitate agricultural exports
- improve farm site safety
- Category III positioning systems may be suitable for general water resource management, but for more precise applications, Category II or even survey grade tools will provide more useful data, increasing the effectiveness of the data.
- Precision guidance systems can rely on Category III positioning for some aspects such as yield monitoring but require precision grade Category II systems for tasks such as overlap and skip. Category I positioning is needed for automated row-crop management. Equipping users with high performance systems extensively increases the opportunities for increasing operational efficiency.
- As exporting increases, tracking an organization’s efficiency through reliable production and operation information becomes essential to maintaining a profitable business. Precision agriculture systems relying on Category II positioning provides a means to monitor and report efficiency.
Aviation
From early on, the aviation community could see the benefits of using GPS for navigation. What was needed was a monitoring system that could also increase reliability. The result was SBAS networks. Although regional, SBAS coverage areas are very broad, allowing users from many industries and areas to take advantage of the free correction services. As a result, many companies produce aviation GPS receivers that are SBAS ready. As most aerial applications require aircraft to maintain separations of hundreds of meters for safety, Category III receivers are often more than capable of the job. However, there are applications where precision is still important, for tasks such as aerial crop dusting and fire fighting, and Category II systems are the answer.
Marine Navigation
In history, a strong economy required trading. Since much trading was done over seas and oceans, navigation has always been important to economic success. The same is true today. Using GPS in marine applications offers low cost navigation to all users by providing accurate position and speed information. Operators can save money by saving time and fuel.6 The improved efficiency benefits everyone with lower shipping and insurance costs as well as the environment (figure 3).
SBAS enhances safety on the water much like in the air. Category III receivers are affordable on the smallest of vessels, providing safety to users who otherwise could not afford solutions. When using SBAS the improved accuracy makes low cost Category II receivers suitable for many workboats, where precision matters. Applications range from sweeping and dredging to automated buoy positioning.6
Railway Management
Another cost effective means of transportation is by rail. While trains do not need satellites to navigate, there are still many advantages to using at least a Category II or III receiver for scheduling, collision avoidance, and maintenance.7 Scheduling generally does not require precise positioning but does require an integrated solution. Category II receivers typically offer easy integration at an attractive price. Collision avoidance requires sub-meter performance and high reliability to determine which tracks the trains are on, and what speed and direction they are going. This clearly requires SBAS enabled Category II receivers. Maintenance information about track conditions can be collected by trains equipped with GPS and other sensors to keep the tracks in proper repair.10 This also requires Category II SBAS receivers.
Some rail systems are part of other site facilities such as mines and port facilities. Using SBAS enhanced GPS in such places is just one important piece to achieving better efficiency and optimization for the entire operation.
Port Handling
Sea ports are the gateways into and out of countries. Goods travel by truck or train to the port where they are loaded onto boats. Thousands of containers pass through the port every day and it is surprisingly easy to misplace a container. GPS and GIS are used to track where every container is placed in the yard. This makes them easy to relocate when it is time to ship. When combined with other identification technologies like RFID or barcodes, smart port systems simplify on-site container storage, reduce container retrieval time, and reduce the time ships are in port.9 This improves port efficiency. Even after only a few months of operation, one port in China reported a cost reduction of 8%, and a 10% increase in productivity.6
Figure 4: Port facilities can be congested and have many signal obstructions
Even though a container is large, its position has to be known to 0.5 meters or better to prevent the lift cranes from driving down the wrong aisle to retrieve it. As well, there are many places in the port where there are obstructions to satellite visibility (figure 4). The receivers used have to recover from signal outages and settle to sub-meter accuracy within a very short time. Combined with the 0.5 meters accuracy requirement, Category II receivers are an obvious choice. Without SBAS, ports must setup their own base station and use radio links to each vehicle to receive corrections. With up to 300 vehicles in a large port, the additional equipment costs and complexity can be considerable.
Results and Discussion
Given the need to succeed through efficient, cost effective programs, emerging applications can benefit greatly by employing a variety of GPS technologies and techniques. The most significant gains can be realized when an SBAS correction service is available in the region. Many applications can take advantage of the cost savings available by not having to utilize alternate correction services and also easier learning curves with the simplified equipment. Most consumer priced GPS systems will see a small improvement in accuracy when SBAS is present, while high-end RTK survey systems will not benefit at all. The Category II products, (the precision positioning systems), will benefit the most. They will improve from two to three-meter accuracy up to 0.3-meter accuracy.
Having had the opportunity to work with many different GPS receivers, the authors note that the Crescent series of GPS receivers offered by Hemisphere GPS are capable of the precision positioning systems discussed in this paper. There are very few other systems offered by other manufacturers that can meet this accuracy. For a look at the different products available and their specifications, please visit the company’s website at http://www.hemispheregps.com.
References
- Schwinger, V. (2005). Quality of low-cost GPS for geodetic and navigation applications. Proceedings from Map Middle East 2005. Dubai, UAE
- Green, G. C., Snow, R. W., & Blaha, T. (2004). Low-Cost GPS Survey System Speeds Survey Work In Developing Countries. Proceedings from FIG Working Week 2004. Athens, Greece
- Ad-hoc Expert Group (1998). An Integrated Geo-Information System with Emphasis on Cadastre and Land Information Systems for Decision Makers in Africa. Proceedings from the United Nations Economic Commission for Africa. November 1998: Addis Ababa, Ethiopia
- Department of Agriculture & Cooperation, Ministry of Agriculture, Government of India (2007). Section 13: Imports/ Exports/Inflation Rates. Agricultural Statistics at a Glance 2006-07. New Delhi, India
- Pandey, M.M. (2007). Present Status and Future Requirement of Farm Equipment for Crop Production. Status of Farm Mechanization in India. New Delhi, India: Department of Agriculture & Cooperation, Ministry of Agriculture, Government of India
- National Space-Based Positioning, Navigation, and Timing Coordination Office, Applications – Marine, Retrieved December 31, 2007, from http://www.gps.gov/applications/marine/index.html
- National Space-Based Positioning, Navigation, and Timing Coordination Office, Applications – Rail, Retrieved December 31, 2007, from http://www.gps.gov/applications/rail/index.html
- Wang, B., Wei, Q., Tan, Q., Yang, S., & Cai, B. (2004). Integration of GIS, GPS and GSM for the Qinghai-Tibet Railway Information Management Planning. Proceedings from Istanbul ISPRS 2004: International Society for Photogrammetry and Remote Sensing. Istanbul, Turkey
- Fearing, R. C. (2004). 1.221J Transportation Systems Assignment 1: Transportation System Issues, Port of Long Beach, California. Massachusetts, USA: MIT Department of Civil and Environmental Engineering