No utility can deny that surveying plays a crucial role in the design and placement of its infrastructure. Maybe not so much for the small jobs, but the placement of more than two poles generally requires some means to provide a straight line. Larger projects such as a new transmission circuit, distribution feeder extension or relocation due to roadway construction require a means of collecting accurate data from the field for design and then transferring that design accurately back to the field for construction. Traditional surveying methods have been used for centuries, but emerging technologies have begun to ease the pangs of surveying by utilities. The use of survey-grade GPS technologies has rapidly changed the approach of one utility.
GPS Background
The Jackson Energy Authority (JEA) is a multi-utility municipal providing water, wastewater, natural gas, propane and electricity to approximately 35,000 customers, as well as offering telephone, Internet and cable services through its fiber-to-the-home network. JEA's history with GPS equipment first began with the other underground utilities rather than electric. In 2002, JEA management decided it was time to begin collecting survey-grade data (positions accurate to 1 cm or less) on underground infrastructure.
A single base station and receiver/data collector (or rover) was purchased, and within a year, another rover had been purchased. The first pieces of data collected were locations of existing features such as manholes, water and gas valves, and water meters. Soon rovers were deployed to construction crews and inspectors for the purpose of collecting positions on water, sewer and gas mains during new installations. The vision of JEA management was to not only exploit the accurate X-Y location of facilities but also the vertical or Z-coordinate.
Although the original intent was to leverage the equipment for future locating of underground infrastructure, the engineering department saw an opportunity to use the survey-grade equipment as a data acquisition device for project design as well as a field-staking device once the design was complete. This was hastened by the increased sharing of digital files from surveyors, developers and designers. Soon the engineering department was using the equipment, coupled with survey-accurate digital drawings, to perfect the design and field-staking process. Aside from accuracy, several other benefits were realized as a result of implementing survey-grade GPS equipment.
How Does It Work?
Nearly all people have experienced a GPS-enabled device at some time — whether in their automobile for navigation instructions or on their smart phone to find the closest Italian restaurant. These devices operate autonomously, meaning they receive signals from a constellation of 24 U.S. military satellites and from no other source. The signal is time stamped and transmitted at the satellite, and the GPS-enabled device has the ability to triangulate itself based on the time it takes for the signal to reach it from the satellites overhead.
Autonomous operation is, at best, only accurate to approximately 50 ft (15 m). Additional devices are required to overcome the inaccuracy. This is the role of the base station. It is its own satellite receiver, placed at a fixed location. The base station compares its known location to its calculated GPS location and sends a correction factor through some means of communication to the rover. Because of this, the rover must remain within a 40-mile (64-km) radius from the base station. This position correction between the base station and rover is known as real-time kinematics (RTK). Without this base station correction, the rover would be forced to operate autonomously with a much lower accuracy.
Changing Technology
JEA's original equipment purchase was quite expensive. The base station came with a price tag of approximately US$65,000, while the rovers averaged $25,000 each. The base station required a PC and an airlink modem to send its RTK signal to the rovers. The rovers consisted of a saucer-sized satellite receiver, mounted on a surveying rod, connected to a backpack that housed the modem and batteries. Wires and cables connected the backpack to the GPS receiver and data logger. The data logger itself was not very intuitive, presented no graphics and did not allow for entering attribute information at the GPS positions collected.
To overcome these hurdles, JEA began speaking with multiple vendors to find equipment suited for its engineering needs. With the help of GEO-Jobe GIS Consulting, JEA selected Trimble's GeoXH data logger and R8 GNSS satellite receiver. The new receiver does not require a backpack for power or modem. The RTK signal is received from a cell network rather than an airlink modem. Also, communications between the cell phone, satellite receiver and data logger are all accomplished by Bluetooth connection — no wires with which to contend.
Furthermore, the GeoXH data logger offered a touch-screen mapping display and the ability to collect attributes for each feature collected. The mapping display allows the user to navigate within a version of the CAD drawing on the data-logger screen. Collecting attributes at each position allows better field data to be attained during a project's initial survey. Another helpful function is the unit's ability to collect line features and point features. And finally, Trimble's Pathfinder Office software makes migration of drawings between the data logger and PC seamless.
In 2009, JEA's base station crashed and, due to obsolescence, could not be repaired. By that time, there were several independent base station networks operating in the multi-utility's service territory. The evaluated cost of license subscriptions was much cheaper than purchasing another base station. JEA chose to forego the expense of another base station and spread its rover subscriptions over two of the available networks for redundancy and reliability.
Overcoming Skepticism
With any change comes resistance. JEA took several steps to build its own trust with the technology as well as those affected by it. First, JEA engineering field-staked several projects using both traditional methods and GPS equipment. The redundant effort allowed engineering to gauge the potential impact GPS surveying and staking would have on time savings and the reduction of manpower. It also was a great test to benchmark GPS accuracy and reliability. This built trust among those in the engineering department that GPS surveying was dependable enough to become the new norm.
Then the task was to develop trust with those potentially most affected — the construction crews performing installations. It was realized that a single stumble could discredit the efforts of engineering. On several occasions, engineering was able to work with crews, allowing them to help field-stake locations and assess on their own the ease of use and resulting accuracy. As more and more completed projects ended with satisfactory results, acceptance grew.
The Utility Benefit
Survey-grade GPS technology offers many advantages over traditional surveying methods. First, traditional surveying requires two people, entails the time-consuming task of referencing benchmarks and back sites, and is limited by line of sight. GPS equipment requires no second person and is not limited by line of sight (although it can be limited by foliage or tall buildings). GPS surveying also allows the user to collect greater detail for design. Detailed attributes can be collected at each feature, Z-coordinates are collected at each location, aiding with profile design, and line features greatly clarify data.
The ability to leverage digital drawings from other surveyors, developers and designers is another great benefit. More commonly, a digital drawing is used as the utility engineer's base drawing. This, of course, requires the source drawings be geo-referenced. The engineer's design is drafted and migrated to the data logger, and there is often only a single field mobilization for staking. Another utility benefit is the ability to make on-the-fly adjustments in the field. The data logger and its software allow for basic drafting functions in the field and minor alterations to the design can be accomplished in the field rather than back at the office. Upon design completion and field staking, the project remains in the data logger until erased by the user.
Many times, a utility must make recurring visits to the construction site to replace stakes at disturbed or compromised locations. Surrounding construction activities, site excavation and mowing practices are often to blame, and the GPS user can quickly navigate back to the previously identified location. Finally, the ability to share design files with drafters for uploading into geographic information system applications greatly reduces the drafting time and entering of attribute data.
Becoming the Standard
At JEA, high-accuracy GPS equipment has rapidly replaced traditional tactics for surveying and field staking. It is not a perfect fit for all applications, but it has quickly evolved as the go-to means for data acquisition and navigation. The equipment is now used extensively for design by each of JEA's utilities and has proven to be both rugged and reliable. Although the equipment's capital cost is higher, it has afforded JEA engineering the convenience to operate more efficiently, with less manpower and with greater accuracy.
GPS equipment has allowed JEA to better leverage digital mediums to its advantage from project beginning to end. Overall, survey-grade GPS has become a staple in JEA's tools of the trade to provide the lowest-priced utilities possible, by the most efficient means available, for its customers.