Enhancing the use of GPS survey systems.

Like many traditional civil engineering/land surveying firms, Miller, Triplett and Miller Engineers (MTM) has a notable history and a dedication to excelling in business. Located in Birmingham, Ala., MTM was founded by Joseph A. Miller Jr. in 1961. Since then, the company has continued to provide high-quality professional services to a variety of clients.

Miller's education and impressive background made him well-suited for his own business venture. He obtained his degree from Alabama Polytechnic Institute (now Auburn University) and served in the U.S. Army Corps of Engineers as an intelligence and reconnaissance officer. After leaving the military, he worked for the Alabama Highway Department as assistant project engineer and division office engineer. Following five years in the transportation industry, he worked for two local private firms before making his final career move to his own enterprise.

While Miller retained overall control, his business has involved several other key members over the years. In 1967, Miller's son Joey began work at the firm as a rodman and followed in his father's footsteps by graduating from Auburn University with a degree in civil engineering. Another of Miller's sons, James, now a registered professional land surveyor, also worked his way up over the past 20 years, from rodman to party chief. In 1972, John B. Cornett, PLS, began working for the firm as a rodman. He's worked his way up the ranks since then. For about 10 years now, Cornett's responsibilities have included coordinating all of our survey crews and overseeing all land surveying jobs. With a solid team in place, Joseph Miller retired in 1999, turning control of the firm over to his son Joey. In his time, Joey has seen his own changes within the firm.

Bryan Pressnell sets up Topcon's HiPerLite+ base station at the Calera site.

MTM's Project Résumé

Over the years, MTM Engineers has logged an impressive history of diverse projects in almost every aspect of civil engineering and land surveying. The company's scope of work has included projects for the transportation and utility markets, and storm water design. Site planning services have included one of the largest industrial parks in Birmingham and one of the largest commercial developments in the area. MTM employees have served as consulting engineers for a municipality and a water authority, designed several hundred residential subdivisions totaling more than 11,000 individual lots, and completed more than 20,000 mortgage loan surveys. Additionally, producing ALTA/ACSM detail surveys has become one of the company's specialties.

I came to work for MTM in June of 1998. I was a sophomore in the civil engineering program at the University of Alabama, Birmingham (UAB) and was looking for a part-time job in my area of study. When I started with the company, I delivered drawings and researched information for surveys and engineering projects at local courthouses and utility companies. Within one year I made the jump to a part-time draftsman and began doing some preliminary design work. By my senior year my design workload had increased and I was becoming an integral part of MTM. During this time I gained valuable survey experience when I went to project sites with our field crews on days when they were short-handed. This experience enabled me to become familiar with MTM's survey methods and equipment.

Today, Joey, John and I share office and design responsibilities. We have three experienced field crews that perform our land survey and construction layout tasks. The three of us all share fieldwork responsibilities from time to time when vacation days or illness impacts our field personnel.

We typically run a three-man crew and use total stations for data collection. Since our workload increased dramatically over the past few years, we began to fear losing jobs because we couldn't keep up with the demand. We realized it was time to look into obtaining additional survey equipment that would help us to be more productive.

Pressnell and Roger Wheeler of Hayes Instrument Company buried Topcon's rovers deep in the woodline to evaluate time elapsed in obtaining a fixed position.

Introduction to GPS

In the fall of 2003, we purchased our first GPS survey system. Roger Wheeler, sales representative with Hayes Instrument Company in Shelbyville, Tenn., recommended the Topcon (Livermore, Calif.) HiPer Lite, a cable-free integrated RTK GPS receiver. This model was reasonably priced and had the range and precision we needed. Roger allowed us to demo the system on a couple of jobs; soon after, we purchased it. After seeing its performance in the field, we were confident that it would speed up data collection and survey tasks. With our overloaded fieldwork schedule, it would be a welcome addition to our survey instrument inventory.

After logging some field time with the HiPer Lite and experiencing the increased productivity we could achieve with the new system, we began to explore other aspects of GPS technology. Roger informed me that the Topcon HiPer Lite was available with GLONASS capabilities, a feature we were unaware of. He explained that, for our survey purposes, access to both GPS and GLONASS satellites would increase our productivity and accuracy on sites with marginal to heavy canopy (tree cover) or other types of sky view obstructions. He also explained that better satellite coverage and distribution would increase our horizontal and vertical precision.

To explore the advantages that Topcon's proprietary GPS+ (GPS + GLONASS) option could offer us, I downloaded the Topcon Occupation Planning software from the company's website. This program allows us to graphically view the number of available satellites for a selected date and time range, and calculates several different Dilution of Precision (DOP)* factors. To use the software, a satellite almanac must be referenced. There are two ways to acquire an almanac. It can be collected in the field with a base or rover antenna, or it can be downloaded from Topcon's website. Topcon's version is updated every few minutes, and a new almanac is uploaded daily. It also includes data for the Russian GLONASS satellite system.

The Occupation Planning software is a great addition to our office and has helped us to coordinate the best time of day to do field work with our GPS system. By knowing the number of satellites we can expect to access on a particular site at a certain time of the day, we've eliminated unproductive trips to the field. Using this mission planning tool, it was easy to see that adding GLONASS satellite capabilities would extend our fieldwork opportunities to cover time periods with low GPS satellite coverage.

We also began to understand that Topcon's GPS+ option would allow us to attain quicker position fixes on sites with obstructed sky views. Roger provided me with a demo HiPer Lite+ system-the system that accessed both satellite systems-so I could experience the difference firsthand.

An Initial System Comparison

To perform a field evaluation of the two systems-the HiPer Lite and the HiPer Lite+-I decided to go to a site that I knew had some marginal to heavy canopy. Because of my extensive experience using our HiPer Lite system, I could spot locations that I knew would have slow response times when collecting data.

I went to the site and set up the HiPer Lite and HiPer Lite+ base antennae side by side. I then set up each of the rovers and began my comparison. Immediately, I noticed that the HiPer Lite+ system was accessing three to four more satellites than the HiPer Lite system. I decided to take two sets of shots in marginal canopy and two sets of shots in heavy canopy. I recorded the time it took for each rover to attain a fixed position at each location. Back at the office, I took an average of the four sets of side-by-side shots. The HiPer Lite+ attained a fixed position in 78 percent less time than the HiPer Lite.

I was very impressed with the results from the HiPer Lite+. The increased number of satellites greatly decreased the waiting time for the unit to become fixed. With these results in mind, I decided to compare the two systems on one more site.

Pressnell and Wheeler compare satellite sky plots; Topcon's HiPer Lite+ tracked a total of 13 satellites.

A Follow-up Comparison

I planned a trip to a church site in Calera, Ala., with which I had prior experience. We had previously prepared a topographic survey there for development planning purposes. The majority of the tract was an overgrown field with vegetation approximately 4 to 6 ft high; it also contained a densely wooded area around a creek. Our field crews had other commitments and were behind schedule, so I performed the data collection for the topo myself. I took one of our crew members with me to cut a path for me to travel through the heavy underbrush. Using our HiPer Lite GPS-only system, I collected about 75 percent of the shots at the site in a relatively short period of time, especially compared to what it would have taken for a field crew to survey it conventionally with a total station.

The wooded area around the creek concerned me. This area ran along a southeast-northwest line. I knew that collecting shots in and around this area could be slow because of the obstructed sky view. I tried a couple of shots, but soon realized that efforts in this area would take some time. I was on a tight schedule, so I decided to send our other field crew out with a total station at a later date. I collected data from the other areas of the site and returned to the office.

Roger agreed to bring the HiPer Lite+ demo system to the church site for my second evaluation. We met one morning at 8:30 when sky conditions were clear and the air temperature was in the low 90s. Setting the base antennae went quickly. We checked the satellite status prior to advancing toward the wooded area; nine GPS satellites were available. When we reached the woodline, we immediately noticed that the HiPer Lite+ system obtained a fixed position within a few seconds. Our GPS-only rover reached a fixed position within one minute. We moved to a couple of other spots along the creek and experienced the same result. I was also impressed with the fact that the GPS+ unit stayed fixed while we made minor adjustments to our positions. When we came back to the antenna site at 10:00 a.m. to disassemble it and leave, we again monitored the satellite sky plot. A total of 13 satellites were available: eight GPS and five GLONASS.

A "Plus" Is a Bonus

These two side-by-side comparisons convinced me that upgrading our GPS-only system to include the GLONASS option would be a benefit to MTM Engineers. The two trial locations are typical of the challenging sites we have in our area of Alabama. We could have eliminated the extra trip to the Calera site if we had been using Topcon's HiPer Lite+. With our busy schedule and heavy workload, the + system offers us a solution for accelerating data collection and construction layout tasks. As MTM prepares for the future, we see how GPS equipment is becoming an integral part of land surveying. From our experience with Topcon's HiPer Lite and HiPer Lite+ products we feel we are preparing ourselves for future changes in land surveying methods and equipment while continuing to provide high-quality professional services to our clients. Mr. Miller is sure to be proud that MTM continues to uphold the legacy he created of excellence in business.

* DOP concerns the geometric strength of the figure described by the positions of the satellites with respect to one another. Four or more satellites must be above the observer's mask angle for the simultaneous solution of the clock offset and three dimensions of the receiver's position. But if all of those satellites are crowded together in one part of the sky, the position would be likely to have an unacceptable uncertainty. That uncertainty can be represented by a number called the geometric dilution of precision (GDOP). GDOP represents the uncertainty that may be expected in the three position coordinates and the clock offset from a particular configuration of satellites. And when the GDOP is high, accuracy suffers. From Jan Van Sickle's GPS for Land Surveyors.