September 1, 2009
The Commonwealth of Puerto Rico has experienced rapid economic growth and dramatic social changes since its current political structure was established in 1952. Almost 75 percent of Puerto Rico’s land mass consists of hills and mountains too steep for sustained commercial farming or substantial tourism--a traditional economic staple of Caribbean islands. Today, the main economic activity on the small island is manufacturing. Some estimates indicate that manufacturing contributes 40 percent to the territory’s gross domestic product, while tourism and agriculture contribute just 7 percent and 0.5 percent, respectively. Manufacturing is also the largest employer of the almost 4 million inhabitants of the island; the pharmaceutical industry alone employs almost 28,000 people. According to the U.K.’s Financial Times, 164 of the Fortune 500 companies have significant operations in Puerto Rico.
Due to the influx of high-tech companies like Microsoft, a reliable source of energy is essential for progress. The Puerto Rico Electric Power Authority (Prepa), a public corporation and government utility agency established in 1941, has been instrumental in the industrial development of the island. By maintaining existing infrastructure and increasing the availability of electricity through new projects, Prepa plays a key role in preparing Puerto Rico to take advantage of future economic opportunities brought about by globalization, its relative social and political stability within the region, and its strong historical and political ties to the United States. However, on an island where the natural habitat impedes even the most simple of surveying chores, building an electrical system can be a daunting task.
Establishing the Network
The largest cities and the most populous towns of the island surround the verdant Cordillera Central, or central mountain range, and form a collar along the coastal areas to the north, east, south and west. New infrastructure is needed to support population and economic growth; however, the lush countryside pushes to the edges of populated areas and makes the installation of such infrastructure arduous and slow. Several years ago, Eduardo Goitía, land surveyor manager for Prepa, began exploring whether GPS equipment would help the organization address these conditions and acquire the rights-of-way needed to establish the location of new power lines and towers.
In 2007, Miguel Rodríguez Sáenz, Central America sales manager for Topcon Positioning Systems, flew to Puerto Rico from Costa Rica and met with Carlos Cotto, Topcon sales executive with Art-Draft Authority, one of the largest suppliers of GPS equipment on the island. Together they met with officials and executives from Prepa. After listening to the presentations and conducting his own evaluations, Goitía determined that the Topcon equipment would allow Prepa to achieve its goals.
To help Prepa address its surveying needs, the Topcon dealer supplied the organization with four network stations consisting of Topcon NET-G3 receivers plus A1 antennas and accessories. (Another GPS system that Goitía evaluated would have required six stations to achieve the same coverage.) Art-Draft Authority also supplied Prepa with GR-3 receivers, which doubled as the rovers necessary for providing precise positions with graduated accuracies. The equipment was rated to meet the project accuracy requirements of no more than 3 centimeters horizontal and vertical and a maximum of 1 centimeter horizontal. The top-of-the-line Topcon GNSS receivers have a dual-communication system that uses both digital radios and cellular technologies for an extended range, and the accompanying FC-120 controllers use TopSURV 7 Complete software.
Working with Topcon networks and OEM sales staff, Cotto and Sáenz−along with Goitía and Prepa surveyors John N. Hernandez, Luis Maldonado, Nortman Orsini and Rafel Torres−conducted preliminary studies to select the appropriate locations for antenna placement. The team considered the availability of communication networks and fiber-optic cable at each site, the presence of vertical obstructions, and the location of each antenna in relation to the shape of the island. The team then performed the work of installing the antennas’ component parts. “It took one day to install each antenna,” Cotto says.
The antennas communicate to the main server through fiber-optic cable. Through the use of SIM cards, surveyors can access the Internet on the FC-120. This capability provides the same range as with radios but with faster access and less signal latency. Prepa employs strict security protocols to avoid unauthorized access.
Hernandez and Orsini gathered data over four days of static observation in five-and-a-half-hour periods. The positions of the antennas were then validated by data collected in 24-hour cycles for 40 days, which was the amount of time deemed necessary to gather the precise ephemeris observations required to tie this network to the Puerto Rico NGS B-order network (the higest order established on the island). The data were subsequently processed by Topcon Tools v7 office software using the Geoid-2003 model. Torres did the computations and analysis, and Maldonado provided logistics of positioning, installation and configuration of the antennas.
After the precise positions were established, the team used the GR-3 rovers in tests to determine the best Internet data supplier with which to establish an Ethernet connection for the network stations. Once the work was completed, Topcon’s staff members trained Prepa’s surveyors in the use of the equipment.
The new network covers more than 75 percent of Puerto Rico. According to Cotto, “The system is consistently precise at 1 centimeter horizontal and 3 centimeter vertical.” While this is an average of the surveying precision afforded by the stations, Prepa surveyors have been able to attain mapping precisions within millimeters depending on the position of the satellites.
Time is Money
The precise mapping of the network gives Prepa greater accuracy in its right-of-way acquisitions. Despite the characteristically lush Caribbean vegetation of the island, surveyors can now determine the location for installing new equipment with greater speed and save valuable time in the collection and management of data compared to static GPS and classic surveying methods. “Now, other divisions of Prepa are interested in using the network for their projects,” Sáenz says.
In May 2009, Prepa surveyors performed various tests with the GR-3 using the antennas in VRS and RTK modes. At the Costa Sur thermoelectric terminal in Guayanilla, surveyors mapped the location for an underground pipeline. Measurements of various points were taken and recorded using the Topcon FC-120. When comparing measurements, surveyors realized that differences in elevation and distance fluctuated by millimeters. They repeated the measurements using a Topcon GTS-700 series 1 total station and then compared the differences in distance and elevation between two points previously established by the VRS system. “The results surpassed our expectations as we observed that the differences were no more than 5 centimeters,” Goitía says.
The time saved on such projects directly benefits the authority’s bottom line. “This surveying equipment shortens the time it takes to install a base line,” Goitía says. “It is a continuous process of saving both time and money. Installation work that used to take months to complete is now done in a matter of weeks, and work that used to take a couple of weeks is done in a matter of days--if not hours.”