Point of Beginning

A Powerful Network

August 29, 2008
A national geodetic network is helping Costa Rica meet renewable energy goals.

Rodríguez uses several generations of Trimble GPS equipment, including 4000SSi, ProXR and R7 receivers, GeoXH hand-helds, and TSC1 and TSC2 controllers, to ensure accuracy at all dam project sites. (Shown is a TSC2 controller with an R8 GNSS receiver.)


Rodríguez uses RTK methods where possible and falls back on a total station (not shown) when necessary.

Costa Rica is a small country; at 19,960 square miles, it takes up less space than West Virginia. But Costa Rica has lofty goals to match its mountainous terrain. It was the first country in the world to abolish its army constitutionally in 1948, and the Costa Rican government has announced that it would like to be the world’s first carbon-neutral country by 2021. Renewable power is an important part of this vision, and the country is blessed with substantial geothermal and hydroelectric resources.

However, renewable power depends on accurate geolocation. Hydroelectric power, for example, can be unprofitable if elevation information is incorrect, and efficient power transmission from unmovable power sources like geothermal sites depends on accurate distance estimates. That’s why the Costa Rican Electricity Institute (ICE), the agency that oversees 96 percent of the country’s power generation, including hydroelectric, wind power, and geothermal plants, is highly motivated to locate assets and resources efficiently. ICE is also responsible for establishing and maintaining all of Costa Rica’s power transmission lines--a task that requires excellent positional resources nationwide.

Yet the Central American country, while small, faces “large cartographic challenges,” says Rody Rodríguez, a GPS administrator for ICE. Geodetic and cartographic challenges arise from several sources, principally the land itself. Densely wooded and highly mountainous, Costa Rica also has a lot of volcanic and geothermal activity. Applying datums consistently is difficult, and mountains and volcanoes can cause gravity anomalies that have frustrated attempts to build large-scale networks with conventional equipment. In addition, a confusing proliferation of datums and projections are in use; Rodríguez lists the Lambert North Costa Rica and Lambert South Costa Rica, the Costa Rica Transversal Mercator (CRTM) 90, 98 and 05, and the “Datum Octopeque,” which is based on NAD27 and was made official in 1945.

Developing a Precise Network

The proliferation of datums is offset, ironically, by the absence of an official geoid, although it would certainly help to resolve gravitational phenomena in this mountainous country. Rodríguez himself has made a start in this area, first using Trimble’s GPSurvey software to extend OSU91, a global geopotential model developed by Ohio State University. More recently, he’s been using Trimble Geomatics Office with higher-resolution EGM96 and Carib97 geoids.

But the situation is changing. As of 2007, by official act, the Costa Rican geodetic work is based on CRTM05 (Costa Rica Transversal Mercator 2005) with a datum based on WGS84, incorporating International Terrestrial Reference Frame (ITRF) 2005 (called CR05 in Costa Rica). And GPS equipment has revolutionized Costa Rican surveying.

“My wife says I eat, sleep and breathe GPS,” laughs Rodríguez, who works in ICE’s Basic Studies Department, which gathers data on site conditions throughout Costa Rica. 

For many years, ICE has been building its own high-precision geodetic network that today covers 85 percent of Costa Rica. Converting the system from Lambert to CRTM05, along with densification and verification, has been a high priority of Basic Studies.

“It’s probably the network with the most national presence,” says Rodríguez, “so we want all our work to be based on it, and we want the datum to be CRTM05. Also, a number of large public and private companies have asked ICE for our data so they can avoid building their own networks--so we know we’ve developed a valuable resource.”

Costa Rica’s hydroelectric Pirris Dam site is located 50 miles south of San Jose.

When working on adjustments, Rodríguez combines Trimble Geomatics Office software with ARGE, an adjustment program developed by professors at the National University of Costa Rica, and Program Adjustment Network Deformation Analysis (PANDA), a program developed at the University of Hanover, Germany.

Other networks exist, such as the one administered by the National Geographic Institute (IGN), but Rodríguez says ICE’s network is better suited to the agency’s purposes and he has more confidence in it, thanks to the GPS work.

“Before GPS, all our projects used local control,” he says. “But since 1990, the network and our infrastructure have been growing rapidly, and GPS has helped a lot. Sometimes, when tying into existing networks, we’d find discrepancies due to the crustal movement in Costa Rica and old surveys going back to the 1950s.”

The tunnel to the Pirris Dam site (one of four hydroelectric dams being built in Costa Rica) is 10 meters in diameter and runs 9 kilometers through the mountain; at its deepest point the tunnel is 1 kilometer from the top of the mountain.

With a national high-precision network in place, ICE is able to take on national-scale projects with more confidence. For instance, a 500-kilometer (311-mile) transmission line--”huge for us,” says Rodríguez--now crosses Costa Rica from border to border, a project that would have been daunting without good control.

And Rodríguez adds a personal motivation for establishing and maintaining a national network: “As a geodesist, I’m interested in the technical challenge of producing a consistent system of coordinates that stretches across the zones of Costa Rica without discrepancy.”

Dam Site Survey Work

Recent work on four hydroelectric dams, some in the construction phase and some still in planning stages, illustrates some of the issues surrounding large-scale surveying in Costa Rica.

To ensure accuracy, vertically and horizontally, for all the dam project sites, Rodríguez uses several generations of Trimble GPS equipment, including 4000SSi, ProXR and R7 receivers, GeoXH hand-helds, TSC1 and TSC2 controllers, and several other units. He sets points that densify the ICE network in the hydroelectric project area, using about a hundred points for a variety of purposes, such as construction and photogrammetry control.

Rodríguez says that many points become hard to use over time simply because of the rapid growth of Costa Rican flora. Cutting back plants indiscriminately is not an option; about 23 percent of the country falls in protected preserves, and Costa Rica is serious about environmental concerns--it ranks 5th in the United Nations’ 2008 Environmental Performance Index.

The Costa Rican team aims to produce a consistent system of coordinates that stretches across the zones of Costa Rica without discrepancy. 

To densify, Rodríguez uses two static sessions of one hour each for the highest accuracy points, along with rapid static for points that serve as photogrammetric control. For topographic work, he uses real-time kinematic (RTK) methods where possible and falls back on a total station when necessary--Costa Rica’s dense brush and deep ravines are sometimes too much for global navigation satellite system (GNSS) techniques. As Rodríguez points out, “The dams and the power plants are typically sited, intentionally, in the steepest ravines, and the surrounding mountains block satellite signals.”

RTK work continues during construction, with conventional total stations and levels being used for final work on sensitive equipment installations.

A Grand Vision

For a small country, Costa Rica has achieved a lot, and it continues to move toward its goal of becoming the world’s first carbon-neutral country. With its many natural resources, not the least of which is abundant renewable energy, Costa Rica is well positioned to realize its national vision. ICE aims to develop these resources responsibly and efficiently, and it has found that a nationwide, high-precision geodetic network is an important part of any plan.

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