Infrastructure Modernization Inspires Innovative New CAD/GPS System
By Trimble Navigation Ltd.
Keeping tabs on a 414-square-mile water and wastewater system–the largest in the Southeast–is no mean feat. When the Miami-Dade Water and Sewer Department (MDWASD) began its 10-year, $1.1 billion upgrade project in 1992, the task became even more daunting. Technology was a big part of the solution.
To this end, MDWASD turned to Woolpert LLP, a Dayton, Ohio-based consulting/engineering and GIS firm specializing in water, sanitary sewer and stormwater infrastructure management. With Woolpert, MDWASD is developing the framework for a comprehensive utility information management system by using global positioning satellite (GPS) and GIS methods.
Woolpert, in turn, collaborated with Trimble, Sunnyvale, Calif. With Woolpert`s seasoned input–the firm has used Trimble GPS receivers for 11 years, and has 18 dual-frequency Site Surveyor SSE 4000 and Site Surveyor SSi 4000 units in-house–Trimble modified its 4000 Series receiver technology to create a specialized real-time kinematic (RTK) GPS receiver. The RTK processes centimeter-level accuracy in real time. Now christened the GPS Pathfinder RTK with Aspen (Trimble`s field-data collection software), the new unit lets surveyors collect point features in the field and input them directly to a computer-aided drafting (CAD) package with engineering-grade accuracy. The easy-to-use system loads CAD files, displays scanned raster images and interfaces with the RTK engine.
The $4.4 million field-inventory portion of the project is immense, involving a host of technological challenges: converting MDWASD`s 1,106 water and sewer atlas sheets from paper to multi-tiered digital format;
using GPS surveying to accurately field-verify up to 170,000 above-ground water and sanitary sewer structures;
pulling information from previously created planimetric-based GIS; and
creating GIS layers in an ARC/INFO environment compatible with MDWASD`s current and future information system goals.
“Initially, the challenge of completing the survey in one year seemed ominous,” said Tom Mochty, Woolpert`s GPS services manager. “The GIS data being gathered for Miami-Dade had to be at least 99 percent accurate, which was a real problem with the paper maps we had previously used. With the Trimble receiver, the accuracy was there. The unit`s unique on-the-fly RTK capability eliminated the need for time-consuming post-processing and second sweep efforts; and the pen-based system made paper maps unnecessary.”
“The unit (Pathfinder RTK) gave us huge time savings. Paper maps are unusable in the rain and difficult to use at night with a flashlight. With the Pathfinder RTK, we can work in any weather except lightning, and the backlit display doesn`t require an additional light source,” explained Shane Imwalle, Woolpert`s marketing director. “In addition,” said Imwalle, “a separate paper map is required for each data layer (such as water and sewage layers) and the location of the physical structures indicated on the map may not be accurate. In fact, the structures may not be there at all. With the Pathfinder RTK, we were able to switch easily between layer views on the pen computer, and update in real time structural information for the GIS database being created. Therefore, applications using the new GIS data benefit immensely.”
“The new system gives us the flexibility to create finished mapping in the field by letting us take centimeter-level measurements in real time on a pen-based computer,” said Michael Stanoikovich, Woolpert`s surveying group director. Stanoikovich pointed out that the new system increases speed and accuracy at reduced cost. “The bottom line is, the field-inventory phase is going five times faster and costing up to 50 percent less compared to conventional utility-location surveys,” he said.
GIS Accuracy Improves
The GIS being produced from the GPS data source documents and planimetric data breaks new spatial and cartographic ground. While all GIS are spatial (structures identified in relation to other structures), the MDWASD GIS data collected in the field-inventory phase is also horizontally and vertically accurate to 3.5 cm.
This level of accuracy posed some challenges of its own. “We had to create a solution to make a lot of data easy to interpret at 1-inch equals 300-feet scale,” said Paul Klimas, Woolpert`s GIS division project manager. “We had to devise a way to squeeze symbols for manholes, fire hydrants and the like into the GIS layers while accurately representing each element`s location and network connectivity.” Klimas solved this dilemma, the first time that this has been done, by devising a programming methodology that manipulates symbols and their corresponding attributes to be both cartographically legible and spatially accurate.
Trimble`s Pathfinder RTK allows the operator to automatically record real-time, high-accuracy horizontal and vertical positions every second to better than 5 cm while simultaneously collecting attribute information. The Pathfinder RTK can display existing raster and vector background maps on the field computer, allowing the user to easily navigate to mapping sites quickly and accurately to record position features and their attributes. During data collection, feature symbols are overlaid on the background map for visual reference–a real advantage when updating existing maps or databases. Recording data digitally saves time and eliminates errors that often occur while transcribing paper forms.
The Pathfinder RTK supports the use of laser rangefinders and external sensors, such as digital cameras, magnetometers and echo sounders. Data from these devices is automatically combined and synchronized with GPS positions. With its standard Microsoft Windows operating system, most notebook and pen-based computers can be used.
This article was submitted by Trimble Navigation Ltd., Sunnyvale, Calif., a developer in the emerging commercial markets for GPS satellite-based navigation, positioning and communication data products. These products are sold worldwide for diverse applications including land and hydrographic surveying; mapping/GIS data acquisition; agriculture; military; general, corporate and commercial aviation; marine navigation; vehicle tracking and communications; and mobile GPS.
Woolpert LLP GPS crews utilize Trimble RTK with Aspen as part of MDWASD GIS development in conjunction with upgrade of water and wastewater system.
The Pathfinder RTK allows operators to record real-time, high-accuracy horizontal and vertical positions to within 5 centimeters every second.