Global Positioning System Advances Construction

Remember when Superman flew high in the sky, saw everything going on with his super vision, then headed directly for the trouble spots? His vision was the wave of the future and the future arrived in the 1970s.

The U.S. Department of Defense created a Global Positioning System (GPS) during

those years to allow military ships, aircraft, and ground vehicles and personnel to determine their exact location anywhere in the world in any weather. The system was named Navigation Satellite Time and Ranging Positioning System (NAVSTAR GPS) and now is composed of 28 satellites that cover the globe with location-finding radio signals that can help pinpoint one's location down to a few centimeters.

How does GPS work? Satellites are positioned in space so that they orbit the Earth every 12 hours. At any given time, six to 10 satellites are typically in view from anywhere on Earth. Each GPS satellite transmits a low-power, continuous signal that can be detected and decoded by a GPS receiver. Radio signals are sent from orbiting satellites to Earth. GPS receivers on the ground collect and convert the radio signals into position, velocity and time information. A GPS receiver on a machine computes the exact position of the GPS antennas many times per second, and an on-board computer determines the exact position.

The GPS system is owned and operated by the U.S. military which can disable the system by reducing the accuracy of the signals available to non-military users. The Defense Department can block civilian signals while maintaining encrypted military signals, if needed.

GPS technology brought advances to many industries and offers a range of components that are advantageous to construction. Surveying and mapping use GPS widely because it offers accurate, timely information regardless of obstacles or weather. With a GPS unit, surveyors don't need a line of sight for precise positioning. The system allows surveying and mapping calculations to be conducted by one person, freeing other crew members for other work, and eliminates inaccuracy from lost or unintentionally moved stakes. Surveyors can log and direct topographical detail, stake out boundary and control data to the home base within minutes, then concurrently receive information on their progress.

Dave Steele, surveyor at Veit Companies, Maple Grove, Minn., said all of its excavation projects use machines that have GPS installed on them. "The whole site plan is on the GPS screen inside the machine. We get the correct grade, we know where to take the topsoil off and the plans tell us where the hills are and provide exact information to prepare a site accurately." Machine operators don't have to run the blades because the GPS program runs the blade for them, said Steele. He emphasized that the surveying and excavation work has become easier and faster using machines with GPS that improve every year. As a surveyor, Steele has worked to put in the stakes manually on a site "and you can make mistakes on the location. With GPS, we don't make those mistakes."

Veit Companies uses the SCS900 software on its rovers that shows all the site information that radio signals receive from satellites. The information is installed on a data card along with the project information, and the card is inserted into a computer in the cab. The operator looks at the screen which shows the machine's location on the site and tells the operator the amount of material to be removed. Steele says that his projects have decreased time spent on them by a third.

GPS for surveying started about 10 years ago, says Steele. "Our supervisors don't have to hire outside surveyors anymore. We use our existing work force to operate the machines without having to set stakes."

GPS eliminated the need for constant surveying and mapping updates on the job site for Veit because the data can keep track of a project's progress. Mapping the location of environmental obstacles on construction areas also provides necessary information for contractors about environmental issues for a specific project. Precision in these early stages of a project can help ensure accuracy throughout the construction process. GPS technology has improved productivity and usually pays for itself after a short period of use.

Several types of GPS are sold on the market. At Ziegler, a Caterpillar dealer in Minnesota and most of Iowa, the Trimble GPS system is sold along with Caterpillar's GPS system, known as AccuGrade. Ziegler's customers usually want the GPS on new machines but some customers also ask for the system on machines that are 1 to 3 years old. Typically, machines with installed GPS systems are dozers, excavators, motor graders, and scrapers, said Tim Hoeft, GPS operations manager at Ziegler. He says customers like the convenience and no one has ever returned a system, known as machine control on construction equipment. "We have two types of users coming to buy equipment, site developers and road contractors who are building new highways, on and off ramps, and bridges.

"The contractors use GPS to take readings on the site, compare it to engineers' model and plan, then use the readings to calculate the volumes of dirt that has to be moved and what has to be graded. As they begin to grade the site, the GPS will compare the site with the 3-D model that the computer created for the site," said Hoeft. "The computer calculates how the machine operator should move the blades to finish grading the site."

Hoeft explained that a control module is on board the tractor, a small disk containing the program is plugged into the control module and the program provides directions for particular job site. GPS, when turned on, then takes control over the blade.

"As technology becomes better known, sales of machines with GPS will increase," Hoeft stated. "Both small and large contractors are seeing how the value of GPS adds to their projects, from site development to road construction. Each year, our sales increased because of awareness of the system and we've had repeat customers. Once people have purchased the machines, they continue to buy more."

GPS also has proven its value in structural placement and bridge construction. Large structural pieces, such as bridge sections, can be placed with precision and accuracy using GPS positioning to follow engineers' blueprints. Unlike traditional surveying using laser, long plumb-bobs and theodolites, GPS maintains accuracy when measuring height providing the most accurate method for controlling the vertical line of tall structures. Once built, a tall structure can be monitored using a GPS-based system to compare actual position with design location and calculates any shifts or changes from external forces such as wind. Using GPS in these construction operations means faster completion, reduced costs and more efficient monitoring when the project is completed.

Groundwork construction is another area where GPS has success. With an onboard geographic database, including such information as the location of existing pipelines and utility cables, trenches can be dug without any danger to existing underground networks. The new information is recorded during installation and eliminates the need for surveying during construction.

GPS and wireless communication, when used together, help contractors obtain real-time location of a machine, data on the location of the equipment on a certain day and how it performed, tracking, and monitoring information. In a GPS-equipped machine, the operator can validate operation, which will automatically transmit startup information — such as location, mileage to date, gas level, water level, oil level, and other data — to the home base for assessment and recording. The same information is posted when the machine is turned off.

GPS technology was created to be easy to use. Software in a base station calculates all information received directly and sends it to either onboard or hand-held devices.

GPS technology applied to construction can increase productivity, reduce costs and downtime, and make the construction process more organized and precise. GPS is quickly becoming one of the most productive tools for construction management.