Site Positioning – GPS or Total Station?

Today’s Site Positioning Systems tools that allow a variety of grade checking, positioning and measuring jobs to be performed faster throughout the life cycle of the project. The world has never seen the perfect tool that does it all. In the positioning domain, both GNSS and total stations have earned their place. Especially in the construction and machine control industries, these systems have become commonplace. GNSS has strengths over total stations and total stations have strengths over GNSS. Site Positioning Systems today, have evolved from being high precision complex surveying tools, to being much simpler and easier to use.

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. Depending upon the type of work being performed, there is some combination of price and performance within these scales to best fit a job. But deciding upon the best solution is not always easy or obvious. 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. 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.

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. 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.

With all these variables, how does the potential buyer go about determining the best fit for their particular needs? There is no easy answer. This article has looked at some considerations that should be taken into account. Besides these, many other factors can be considered: Portability, ruggedness, power autonomy, system complexity or ease of use, local support, the ability of the instrument to perform secondary tasks, reliability, governmental regulations, etc.

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 and that it has the flexibility and expandability to handle all the site positioning and measurement tasks you need on your projects. Unless money is no object, there will likely be some type of compromise. Ideally, an end user has access to both the high-end GNSS and total station solutions.

Training on Total Station and GPS is viable at Khagolam Institute of Geoinformatics