GIS Applications for Water, Wastewater, and Stormwater Systems - Chapter 5

CHAPTER 5 GPS Applications GPS technology is no longer limited to determining coordinates. It has become an efficient and increasingly popular way for collecting GIS attribute data for water and wastewater infrastructure. GIS data collection for sewer system manholes using GPS. Copyright © 2005 by Taylor & Francis LEARNING OBJECTIVE The learning objective of this chapter is to discover the applications of global positioning system (GPS) technology in water industry GIS projects. MAJOR TOPICS · GPS basics · GPS applications in water industry · GPS applications in GIS · GPS survey steps · GPS equipment · GPS software LIST OF CHAPTER ACRONYMS DGPS Differential Global Positioning System GPS Global Positioning System GLONASS Global Navigation Satellite System (Russian System) NAVSTAR Navigation System by Timing and Ranging PDOP Positional Dilution of Precision RTK Real Time Kinematic SA Selective Availability WGS84 World Geodetic System of 1984 STREAM MAPPING IN IOWA Application GPS software GPS equipment GPS accuracy GPS data Study area Organization Stream traversing and mapping channel features using GPS Trimble’s Pathfinder Office Trimble Pathfinder Pro XR 1 m for discrete data and 5 m for continuous data Streambank conditions, bottom sediment material and thickness, channel cross sections, debris dams, tile lines, tributary creeks, and cattle access points Neal Smith National Wildlife Refuge, Jesper County, Iowa Iowa Department of Natural Resources In 2000, GIS and GPS were used together to map a 12-km portion of Walnut Creek located near Prairie City in Jesper County, Iowa (Schilling and Wolter, 2000). The objective of the mapping project was to locate channel features and identify spatial trends among alluvial system variables that could be used to identify and prioritize portions of the stream channel and watershed in need of further investigation or restoration. Using Trimble Pathfinder Pro XR GPS equipment, discrete locations (channel cross sections, debris dams, tile lines, tributary creeks, and cattle access points) were mapped to an accuracy of 1 m, whereas the continuous data (bank erosion rates, streambed materials, and thickness) were recorded to an accuracy of Copyright © 2005 by Taylor & Francis 5 m. To record continuous conditions, the GPS equipment was operated in continuous line mode with location recorded every 5 sec. GPS data were exported into a GIS format (ESRI Shapefile), using Pathfinder Office software. Field descriptions of the continuous line segments and discrete features were added to the GPS location information to create various GIS layers. Segment lengths varied from 10 to 50 m. Discrete channel features were located by pausing the continuous line mode of the GPS and taking points at feature locations. Stream survey data were used to model watershed conditions, identify water sampling points, and evaluate and select appro-priate channel-rehabilitation measures. This chapter is intended for professionals in the geographic “positioning” field. It presents applications of GIS and GPS for water industry infrastructure manage-ment. The use of GPS in collecting attributes data is discussed, and methods of data attribution are described. A review of GPS equipment and software is presented. GPS accuracy issues are also discussed. GPS BASICS GPS, also referred to as Navigation System by Timing and Ranging (NAVSTAR), is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense. The Russian government operates a similar system called Global Navigation Satellite System (GLONASS). At the present time, GPS includes 29 active satellites located in 6 orbital planes. GPS systems utilize a constellation of satellites orbiting the earth twice daily (i.e., passing over approximately the same world location every 12 hours) and transmitting precise time and position signals. GPS receivers read signals from orbiting satellites to calculate the exact spot of the receiver on Earth as geographic coordinates (latitude and longitude) referenced to the World Geodetic System of 1984 (WGS84) datum. The signals from at least four satellites should be available to determine the coordinates of a position. Physical obstructions such as mountains, trees, and buildings, and other factors such as satellite malfunction and rephasing operations can restrict GPS signals and degrade GPS accuracy. Ideal GPS operating conditions that provide the best accuracy are listed below (Lyman, 2001): · Low positional dilution of precision (PDOP), a measure of best geometrical configuration of satellites · Good signal strength · Little or no multipath (reflection of GPS signals off distant reflective environment such as mountains and buildings) · Little or no signal degradation because of geomagnetic storms and ionospheric or atmospheric effects The accuracy of GPS coordinates can be increased by applying differential corrections. Differential corrections move user points closer to their “actual” loca-tion. This is done by comparing the user’s new data on unknown locations with the data collected at the same time on a point with known coordinate values (Zimmer, 2001b). The GPS receivers that can receive and apply the corrections in real time Copyright © 2005 by Taylor & Francis are called real time kinematic (RTK) receivers. Non-RTK receivers require postpro-cessing of raw GPS data in the office. In the U.S., federal and state agencies are cooperating to make differential GPS readily available to all users. GPS precision can vary from a few millimeters to hundreds of meters. The required precision depends on the project-specific requirements. The available precision varies with GPS mode (static, RTK, or kinematic), GPS equipment, time of occupation, and location (vegetation, reflection, and buildings). GPS survey cost increases with the accuracy requirements. The typical utility precision standard is 3 to 5 cm. To prevent misuse by hostile forces, the U.S. Department of Defense had intro-duced an intentional error called the Selective Availability (SA) error in their GPS signals. The recent advances in GPS technology had reduced the effectiveness of the SA error. On midnight May 2, 2000, the SA error was removed 6 years ahead of schedule by a presidential order. This event marked an important day in the history of GPS because it increased the GPS accuracy up to ten times. The SA removal has improved the accuracy of inexpensive GPS receivers. SA removal has also increased the accuracy of GPS receivers operating in an autonomous (unassisted) mode without a base station. No significant impact has been noted in the performance of survey grade receivers (Murphy, 2001). GPS technology is making major progress in improving the speed, reliability, and accuracy of the mathematical processes by which coordinates are calculated from the satellite beams (ASCE, 2001). GPS APPLICATIONS IN THE WATER INDUSTRY At the present time, the GPS revolution is well under way. For example, a Mercedes-Benz driver equipped with TeleAid system can press an SOS button to summon a tow truck, police, or ambulance. This button uses GPS technology to transmit the specific location, model, and color of the vehicle. The GPS applications for the water, wastewater, and stormwater systems, though not as dramatic as TeleAid, are revolutionizing the way these systems are designed, constructed, oper-ated, and maintained. Representative GPS applications for the management of water, wastewater, and stormwater systems are: 1. GPS can be used to increase the accuracy of existing system maps by verifying and correcting locations of the system components. Frequent field changes often mean utility lines can be several feet off horizontally and/or vertically from where they appear on the plans. Thus, unless updated frequently, most utility plans, especially in growing cities, are outdated frequently. GPS data collection is no longer limited to collecting coordinates of point features. Now users can bike along a channel to map line features, or walk around a detention pond to map polygon features. 2. New water system or sewer system maps can be created if they do not exist. 3. Water system or sewer system attributes can be collected for populating the GIS database. Copyright © 2005 by Taylor & Francis Surveying Traditionally, people have used geodetic surveying to locate and map utility infrastructure components. Such transit survey required traversing between a known point to the point of interest, which often took several hours per point. GPS has been found to be up to 50% faster than the traditional methods (Anderson, 1998). GPS survey takes only a few minutes or seconds per point. For example, up to 300 points can be surveyed in 1 day, using a GPS survey. A two-man crew with bicycle-mounted equipment can survey up to 500 points per day. The familiar total station is still the backbone of engineering survey work. Although GPS is not a replacement for optical surveying, interoperability between optical equipment and GPS is growing, and GPS is gaining ground slowly among engineers. GPS is an ideal addition to the surveying toolbox for a variety of appli-cations, such as locating the starting point for a new stakeout. The conventional total station survey will require traversing a large distance for this work. GPS can do this work much faster by navigating a person right to the point where the stake should be placed (ASCE, 2001). Fleet Management An efficient fleet management system is essential to improving customer service. A wireless system that uses GIS and GPS technologies can substantially and eco-nomically improve the efficiency of fleet management. An integrated GIS/GPS procedure can be used to track multiple moving vehicles from a command center. It can show the location, speed, and movement of each vehicle on the tracking display. Off-the-shelf mobile devices such as Web-enabled cell phones and personal digital assistants (PDAs) can be used in conjunction with a GIS/GPS to provide the information needed for fleet management, such as dispatching and tracking the maintenance vehicles, generating driving directions, and trip routing. For example, Gearworks customized MapInfo’s MapMarker J Server and Routing J Server to calculate driving directions and travel statistics. A client-side custom mapping appli-cation was created, which communicates with a MapXtreme server to create the data requested by the dispatcher and to deliver the information to the drivers mobile device. This application allows the dispatcher to view a map of the entire fleet to better assign work orders and deliveries, perform real time tracking, and deliver accurate status updates through the Web interface (GEOWorld, 2001). GIS/GPS applications have consistently lowered the cost of fleet management by 10 to 15%. GPS APPLICATIONS IN GIS GPS technology represents a space-age revolution in GIS data collection. It is providing an efficient and increasingly popular way for collecting both the location (coordinates) and the attributes data in the field. The new line of GPS receivers brings Copyright © 2005 by Taylor & Francis ... - tailieumienphi.vn