Equipment Type

Site Positioning -- GPS or Total Stations?

Here are some good general guidelines you can follow.
September 06, 2012

Johan Smet is Director of Technology Consulting and Services for Trimble’s Heavy Civil Construction Division. He joined Trimble in 2004 as Director for the Construction Division. Johan holds an Engineering degree from the University of Antwerp, Belgium, and an MBA from the University of California, Berkeley. 

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Today’s Site Positioning Systems give contractors the technology tools that allow a variety of grade checking, positioning and measuring jobs to be performed faster throughout the life cycle of the project. And in an environment with an increasing use of machine control technology and a decreasing use of stakes that traditionally provide information across the site, they are ideal for providing the supervisor with a view of the “stakeless” job site. Site Positioning Systems today, have evolved from being high precision complex surveying tools, to being much simpler and easier to use. With “contractor” focused software and interfaces, you can take control of your site positioning and measuring needs.

However, one question I hear a lot is “should I use GPS or Total Stations?” There is no one right answer for this, since it really depends on a number of factors. But, there are some good general guidelines you can follow:

GPS receiver based systems are ideal for larger jobsites, and accuracy requirements of 8 millimeters (0.03 feet). Since they depend on satellite signals they work best on sites with a reasonably unobstructed view of the sky. They can be used on a pole or mounted on a vehicle. As a pole mounted system, GPS systems are ideal for moving about on the job site collecting a lot of data—grade checking, measuring volumes, doing asbuilts and more. As a vehicle mounted system, GPS systems provide supervisors with a view of the job site and the job progress comparable to what the operator using machine control sees. Today’s GPS receivers typically track all the major satellite constellations—GPS, GLONASS, Galileo and Compass—and are referred to as “GNSS receivers”. Because they are tracking more satellite constellations, GNSS receivers can provide better coverage and performance even in tough environments—near buildings, under tree canopy or in deep cuttings or mines—than a GPS only receiver.

Total Station based systems provide the highest possible degree of accuracy for site positioning, stakeout, grade checking and measurement. A Total Station-based system has a more limited range than a GNSS-based system and is better suited for projects where accuracy is a key factor. They are ideal for sites where the accuracy requirements are very tight: 3 millimeter (0.01 feet). There are also Total Station systems that use “reflectorless measurement” technology.  Reflectorless technology provides you with the ability to accurately measure a position at a distance without the need for a prism, making these systems ideal for taking volume and progress measurements in dangerous or inaccessible locations.

 

Whether you need the convenience and flexibility of a GNSS-based system, or the tight accuracy of a Total Station-based system, it is equally as important to evaluate the field and office software. Make sure the software has been developed specifically for contractors and that it has the flexibility and expandability to handle all the site positioning and measurement tasks you need on your projects. Also evaluate the positioning tools, controllers and other components for ruggedness, connectivity and overall ease of use.

Of course, the easiest and best way to make these decisions is to consult with your construction technology dealer.

You can read many stories about why and how customers made the decision to implement technology, and what their experience has been, at trimble-productivity.com.

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