Surveying
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High in the Andes mountains of Ecuador, the village of Curingue has no centralized water supply system. The lack of reliable water means villagers face hardship and increased risk of health issues. Enter Engi - neers Without Borders (EWB), who heard about the challenge and be - gan work to install infrastructure that could deliver water to Curingue. The effort required accurate positioning to provide accurate data for At an elevation of roughly 3,600 m (11,800 feet), Curingue is an isolated community. There is no cellular phone service and only lim - ited electricity for the roughly 210 people living there. When EWB proposed to provide a water supply system, they needed data about water sources and the area’s steep terrain. But they soon discovered that there were no existing large-scale maps or geographic information for the area. In order to plan the work, EWB needed to develop ac - curate maps and elevation information. But the remote location had no existing geodetic control points—a complication that could add time and uncertainty to the mapping effort. design and construction. Challenging location Among the EWB volunteers in Curingue was John Hamilton, a U.S. surveyor who specializes in precise measurement and control over large areas. With three decades of experience on four continents, Hamilton has plenty of experience dealing with sparse control and remote locations. A long-time GNSS user, he examined possible approaches to gathering accurate data for the mapping effort. His options included conducting long-observation GNSS sessions and then post processing the data to establish reference stations for RTK. But accessing data from Ecuador’s network of continuously operating GNSS reference stations (CORS) proved problematic. In addition, Curingue’s mountainous landscape made using conventional RTK with UHF radios unfeasible. Precise GNSS in difficult terrain To achieve accurate and reliable positioning, Hamilton used Trimble CenterPoint RTX positioning service, which can achieve survey-grade GNSS positioning (better than 2cm horizontal and 5 cm vertical ac - curacy) anywhere on Earth. Hamilton had gained experience using CenterPoint RTX on projects in the U.S. and Canada and he was con - fident that it could provide the needed accuracy even in the remote Ecuadorian mountains. House to house Using a single Trimble R10 GNSS receiver, Hamilton and his volun - teer colleagues captured the 3D location of water sources that would supply the village. He also collected measurements at sites selected for the water collection point and pump station, an intermediate pump station and a water storage tank located above the village. The team It Takes a Village A surveyor helps bring fresh water to a remote community in the Andes By John Stenmark
worked along the route of the proposed pipeline collecting GNSS data to compile critical vertical profile information for the pipe. They also located ravines and roads that would affect the construction. Finally, they visited each house in the village to collect position and elevation data. “There was absolutely no way to do this without RTX, Hamilton said. “It was very convenient; I didn’t need anything other than my GNSS receiver to do the survey.” Hamilton said they needed roughly one week to complete all the survey work. EWB will use the information to establish a durable, sustainable water supply that will improve the lives of Curingue residents. Work is al - ready underway on the collection point, which includes its own storage tank and pump station. Hamilton is already planning a return visit to Ecuador, where he will work on a similar project in a different village. Correction services will again be his primary tool for accurate GNSS positioning in the rugged and remote terrain. The EWB teams captured the location of buildings in Curingue to support pipeline design efforts. Understanding the difference between RTK, RTN and RTX The advent of GPS in the 1990s enabled crews to establish control in remote locations, but they still needed total stations for topography and stakeout. The big breakthrough came with RTK GPS and GNSS, which allowed for centimeter accuracy in real time. It didn’t take long for RTK to push the use of total stations aside for most oilfield surveying. Both RTX and RTK provide good accuracy, but RTK relies on a GNSS base station and radio data links to send data from the base to the rover. Although RTK is far more productive than total stations, when compared to RTX, RTK comes with lots of logistical headaches, backtracking and costs for equipment and manpower. A similar comparison can be made between RTX and real-time GNSS networks (RTN). RTN is fast and convenient, but only when you are in a specific geographic area served by the RTN – accuracy quickly degrades as soon as you move out of the coverage area. Furthermore, RTN is dependent on cellular communications, which are often nonexistent in remote areas. In the oil patch where projects extend over enormous distances, RTX eliminates both the geographic and cellular dependencies of RTN.
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June 2022 csengineermag.com
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