- SPECIAL REPORTS
- THE MAGAZINE
With 42 years of surveying and engineering experience, The Schneider Corporation of Indianapolis has generated many unique ideas to improve work processes. Schneider, a multi-discipline firm with a staff of 250 employees, has consistently built on ideas in an attempt to find "a better way" of responding to client and community needs. Attempting to stay ahead of the competition requires not only the latest and greatest instrumentation and procedures, but also a dedicated focus to developing and implementing worthy ideas. Central Indiana's rapid growth (it is home to two of the top 50 fastest-growing counties in the country) has required new and faster solutions to typical survey processes. To this end, Schneider has developed many innovations related to Geographic Information Systems (GIS), web hosting, 3D modeling and civil engineering. More specifically, our 91-member surveying department has worked to develop two time-saving, state-of-the-art surveying solutions, one for measure-down procedures, and another for a vast, efficient Real-Time Kinematic (RTK) communication system.
Gathering Infrastructure DataSchneider provides boundary and topographic data, engineering design and construction layout for many residential developments in Central Indiana. On these projects, Schneider's surveyors are often required to obtain accurate infrastructure data related to storm sewers, sanitary sewers, underground vaults, and the like. Stringent design constraints, such as the requirement of sewers to be at minimal slopes, have caused a demand for ever-increasing accuracy. The processes to obtain these accuracies in subsurface elevations has changed dramatically over the years.
While extremely dangerous and not in compliance with many regulations, physically entering sewer manholes to obtain invert elevations is still practiced by some today. One crew member enters the structure while another crew member lowers a steel tape into the structure. The crew member inside the manhole holds the end of the tape on the invert of the sewer pipe while the other crew member measures to the top of casting and records the measurement. This procedure generates an accurate measurement if the invert of the pipe is directly below the opening of the casting. But this rarely happens. So, in earlier times, we would get around the problem of the end of the pipe being offset from the casting by setting a two-foot or four-foot level on the invert of the pipe, extending the invert of the pipe out to more closely represent a true plumb distance. Obviously, this can be a very dirty job if a crew member is in an active sewer-and it lends itself to health and safety risks.
The advent of the collapsible fiberglass rod was the next improvement that alleviated some of the hazards involved with entering sewer structures. Fiberglass rods come in many shapes and sizes. We preferred the 25-foot rod, which was tall enough to measure most sewers but not long enough to be cumbersome and heavy. Using this long rod, the invert elevation could be measured from above the casting without requiring someone to enter the structure. This was indeed a helpful tool, but pipes offset from the casting were still a major problem. We were able to set the bottom of the rod on the invert of the pipe, but the measurement was more than likely not a plumb measurement. Further, trying to figure out the angle of the rod was difficult and time-consuming. This process with the fiberglass rod also made deciphering the pipe size nearly impossible without major guesswork. While no one was required to be physically in the structure, the dirty rod method still wasn't a "fool-proof" one.
To help with the pipe offset problem, one of our senior party chiefs created an offset arm in the late 1980s. This metal arm was attached to the fiberglass rod with hose clamps and was equipped with a torpedo level. This apparatus allowed the user to plumb the fiberglass rod by leveling the torpedo level. This was a great step forward but it only worked if the pipe was offset by no more than a couple of feet from the casting (the length of the offset arm), and if the torpedo level was visible from up above. Again, this approach required inserting the rod into the structure and the structure's contents. Accurate pipe sizes were somewhat easier to establish with this process. Once the invert was measured, the rod and offset arm would be set on top of the sewer pipe and another measurement was performed. The difference between the two measurements (minus pipe thickness) would yield the pipe size.
Despite these improvements, the process of establishing accurate subsurface survey data was still difficult, cumbersome and not nearly as accurate as was often needed. Further, many clients including manufacturing plant owners, increased safety requirements. At Schneider, a decision was made to not allow staff members to physically enter any confined spaces. These safety concerns, along with growing accuracy requirements, led us to obtain confined space and supplied air training through safety management and environmental groups for some of our field employees. We purchased all the necessary safety equipment to hoist an employee on supplied air down to measure sewers. While this process was required in many applications, it proved to be quite expensive and counter-productive for the typical sewer measure-down. As our business grew, we were performing as-builts and measure-downs on approximately 3,000 to 3,500 structures per year. We needed an accurate, safe and clean way to obtain subsurface data that would also increase our productivity.
V.depth-The AlternativeIn early 2002, a measure-down system was created and developed by Schneider personnel. This system, called V.depth, integrates state-of-the-art measuring equipment in a novel device that facilitates quick, easy and accurate measurements to locations at inconvenient or inaccessible depths. The system utilizes the Leica (Atlanta, Ga.) Disto Lite laser distance meter mounted in a precision-engineered, anodized aluminum bracket together with a SmartTool (M-D Building Products Inc., Oklahoma City, Okla.) Builders Angle Finder. V.depth allows pipe inverts and sizes, and countless other inaccessible areas, to be determined accurately with laser-measured precision using a slope measurement and vertical angle. A fully adjustable brace allows the user to establish the tool on a solid base (such as a manhole rim) from which to make the depth measurement.
V.depth eliminates all of the problems encountered from the previous measure-down methods of entering confined spaces and utilizing the fiberglass rod and even the offset arm. The need to enter the structure or to even place a rod or other device into the structure is eliminated with V.depth. Accurate measurements can be obtained without breaking the plane of the casting of the manhole. All measurements are taken from outside the structure. Upon removing the lid of a structure, the tool is set atop the opening. The laser distance meter is turned on and the highly visible laser dot is positioned on the invert of the pipe or to whatever object is to be measured. V.depth remains in that position with a locking screw. The slope distance is measured with the press of a button on the Disto; the vertical angle of that slope distance is established with the press of a button on the SmartTool. The true plumb vertical difference between the top of casting and invert can be easily calculated by multiplying the slope distance from the Disto by the sine of the vertical angle from the SmartTool.
We have found the reliability of V.depth to be unrivaled. There is a maximum 2s error of only Â±5 mm for the laser distance meter and pitch readings in 1/8 inch per foot increments for the SmartTool level. The precision of the measurement on a 10-foot deep pipe in a 4-foot diameter manhole using V.depth is expected to be Â±0.04 feet, although tests reveal repetitive typical precisions of Â±0.01 feet.
We are often required to perform sewer as-builts in the presence of sewer inspectors. These jurisdictional inspectors have great respect for the accuracy and advantages of as-built measurements made with V.depth. This innovation has increased our productivity immensely on subsurface measurements and improved our measurement accuracies, assuring that the survey data we provide can be relied upon more confidently than ever before.
Establishing an RTK NetworkThe first step in establishing an RTK network for our many crews to utilize on a daily basis was establishing a network of permanent base stations. We mounted antennae (we use Trimble Zephyr Geodetic antennae) securely on the rooftops of three of our four offices to be used in conjunction with our Trimble NetRS GPS receivers, however, any manufacturer's hardware utilizing the RTCM correction format could have been used. The receivers were positioned through independent Online Positioning User Service (OPUS) solutions and tied into the state's High Accuracy Reference Network (HARN) through a static GPS network. The resultant residuals between the two methods were minimal, and therefore insignificant. Having our base station positions established, we were prepared to have coverage over the vast majority of the Central Indiana area. The software we currently use to control our network is Trimble's GPSBase, although other manufacturer software can be used. The "missing link" to this setup was a communication system that would satisfy our many requirements.
Accessing RTK Correction DataMuch has happened in the last few years regarding the retrieval of Real-Time Kinematic (RTK) correction data. Only a short time ago, surveyors thought they were on top of the world utilizing an onsite base station with a radio link. We surveyors were able to get RTK initialization up to five miles away in a matter of minutes. Today, cell phones are becoming more prevalent in accessing correction data. But in March of 2003, when we sought to combine voice communication while receiving corrections, data collectors and data controllers were not able to transfer corrections via a cellular Internet connection, a capability now possible through many manufacturers. We had found that the battery life was much greater in a Personal Digital Assistant (PDA) and that we were able to charge spare PDA batteries conveniently inside our survey vehicles via a charging cradle. PDAs have the flexibility to allow field personnel to check E-mail and transfer files to and from the office. We were looking to have a system combining both data capability and voice communication.
V.link-The AlternativeIn April 2003, Schneider personnel developed a solution to the communication system's missing link: a wireless data broadcast network for high-precision real-time GPS applications. The system, called V.link, utilizes RTK correction data output from any of our permanent base stations broadcast to an Internet Protocol (IP) address via DSL, cable or any other broadband Internet connection. This correction data is sent to the PDA via a purely digital wireless network accessed by an aircard from Sierra Wireless (Vancouver, British Columbia, Canada). The card is inserted into an expansion pack on the PDA, which allows a much broader coverage than the traditional CDPD wireless units.
The V.link system can be utilized by any GPS receiver employing the RTCM 104 input/output format. An unlimited number of rover receivers may be used in conjunction with a single base receiver or network of multiple receivers. This is a great advantage because it allows our survey crews to access correction data simultaneously. We currently have 12 GPS receivers using the V.link system, and other clients can access our correction data as well.
V.link offers the unique functionality of a pull-down menu to access a particular base station. Each base station can be named to the user's liking. The latest version of V.link, V2.0 (its third version), allows field personnel to manually enter an IP address and port to access a base station that is not in the pull-down menu. This feature is very useful for in-the-field operations and allows access to any base station not preloaded in the software. The system is also able to access correction data from a Virtual Reference Station network, further adding to its functionality.
The V.link system is housed in a compact, lightweight unit. The PDA is inserted into a rugged, waterproof environmental case (we use an Armor Otter Box, Fort Collins, Colo.) and mounted on a 360-degree rotating system. This Schneider setup keeps the PDA and the data collector conveniently together and allows either unit to be accessible.
We have found the reliability of V.link to be consistent with that of other RTK methods. The system has been extensively tested and used on a regular, daily basis. HARN stations have been verified up to 30 miles away. This coverage has allowed our crews to have "out-of-the-truck" initialization regardless of weather conditions in the vast majority of the Central Indiana area.