- SPECIAL REPORTS
- THE MAGAZINE
Installing a GPS reference station can be an expensive proposition for a small city with a limited budget. And it's often not easy to demonstrate the potential return on investment necessary to persuade city councils to make capital improvements in infrastructure without a clear link to constituent services. Yet the rewards for implementing a GPS-based GIS program are considerable for both private and public users, and we in the city of Rock Island in Illinois discovered an innovative solution to implement one. Its initial purpose was to map all the sanitary and storm manholes plus all of the catch basins and storm water outfalls (flared end section, headwall or straight pipe structures where storm water runs out into a stream, creek, pond or river) within 18 months of the base station being installed. We approached the two nearby cities of Moline, Illinois, and Davenport, Iowa, and asked if they would be interested in sharing the costs of a GPS base station. Situated in the northwest corner of Illinois, at the confluence of the Mississippi and Rock Rivers, the city of Rock Island covers about 15 square miles and is home to nearly 40,000 residents. Located just to the east of Rock Island, the city of Moline also covers about 15 square miles and has a population of about 44,000 residents. Just across the Mississippi River from Rock Island is the city of Davenport, which covers 66 square miles and has a population of about 98,000 residents. Based on positive feedback from both cities, our city council approved funding to buy and install a GPS base station and two rovers in 2002 from our local dealer, Turning Point Systems Group (Chicago, Ill. and Milwaukee, Wis.). It seemed that our productivity soared almost overnight: we achieved an estimated 75 percent time savings in data collection. The cities of Moline and Davenport joined us under a cost-sharing agreement early this year, and the arrangement has worked out very well for all three cities.
Before GPS: Slow ProgressBeginning in 2001, Rock Island's Engineering Department staff members started work on a project to map out the city's complete storm water system and to collect certain attributes. We started doing this with a total station and off-board data collector. Since we had an agreement with Rock Island County for handling all of our GIS data, we collected the data and gave it to the county to store and manage. The county then put the data on our intranet so our people could access the data.
We found that the pace of data collection using the total station was slow. We had to run control to the areas we needed to map from our aerial control points, which always seemed to be a mile away. We ran big traverses off our aerial control points and established our control points to use for mapping our storm system. When we operated on big streets, we could get a lot of shots from one setup, but there always seemed to be one point that was in an alley, making it necessary to set up an extra point. It seemed like we were setting up and tearing down the instrument a hundred times a day. In nine months, we had only succeeded in mapping about 15 percent of the storm system. With more than 15,000 structures to map, we estimated in 2002 that it would take some five years to complete the process using the current methods.
Our initial research indicated that we could increase production by at least 50 percent by switching to GPS. While the potential return on investment in a GPS system seemed clear, budgets are always tight in a small city like Rock Island, and it seemed unlikely that the city council would agree to the expenditure. That's when we developed the idea of approaching the two adjacent cities with a proposal to share the costs of a GPS system. Although they chose not to sign any formal agreements until after we had set up and proven the GPS-based GIS in Rock Island, our counterparts in Moline and Davenport were enthusiastic about the idea. Buoyed by their positive response, the city council of Rock Island voted to approve the budget for implementation of the GPS.
GPS Implementation: Productivity SoarsGPS equipment was ordered in April 2002 and installed in the first week of June. The base station consists of a Leica GPS receiver (Leica Geosystems, Atlanta, Ga.) and two-watt PDL4535 Pacific Crest radios (Pacific Crest, Santa Clara, Calif.). The GPS reference station antenna was mounted on top of our water treatment plant. The concrete block structure created a stable platform and provided excellent satellite visibility to the antenna. The GPS receiver and one of the radio transmitters are located in a locked box inside the building. The radio broadcasts are amplified by a 35-watt radio repeater on top of the water tower at the plant for broadcasting to rovers throughout the city. We picked this location because the water tower is located roughly at the midpoint of the city east to west, and it is at the top of the hill that overlooks the river valley. A radio repeating system was chosen instead of running wires to the top of the tower for two reasons: it was easy to install and less expensive than running high performance radio cable over a long distance. The water tower is about 300 feet from the treatment plant and stands about 150 feet high. We are able to cover a radius of 12 miles easily with no radio dead spots inside the city limits. When Moline and Davenport later came on board, they established mobile repeaters to help them broadcast the GPS signals into areas that our transmitter could not reach. Our maximum coverage area is a 35-kilometer radius from the reference GPS antenna to get the required accuracy.
The GPS base station has been trouble free. The only problem with its installation came when we had to reset the radio repeater after power outages. It was often necessary to climb up to the top of the water tower to turn the radio back on when the power was restored-not a pleasant job even under the best of conditions. The water tower was prone to losing power when there was an electrical storm in the area. Early this year, as Moline and Davenport were preparing to join us in the use of the system, we took the radios down and had the internal surge protector removed so they will automatically turn on once power is restored.
In addition to the base station, we acquired two Leica GS50+ rovers using PDLGFU6 Pacific Crest radios and two MSL-3800 MicroSlate (Armonk, N.Y.) ruggedized pen-tablet PCs to start collecting data. The rovers arrived before the pen tablets, so we got started using the rovers. Our initial goal was to map all the sanitary and storm manholes and to map all of the catch basins and storm water outfalls within 18 months of installing the base station. Within four months, we shot 85 percent of the 15,000-plus structures. During the winter of 2003 we collected almost all of the data of the remaining structures using GPS. That left only about 200 structures to be shot with the total station. Cutting our mapping time from a projected 18 months to just four months translates into a 75 percent time savings.
When the pen-tablet PCs arrived, we used them to collect attributes on the structures that we had already mapped with the GPS rovers. After conferring with the staff at Rock Island County, we decided to buy ArcPad 6 (ESRI, Redlands, Calif.), mobile mapping and GIS software, including the associated customization tool Application Builder to create forms for entering the attribute data. We also interviewed people in our engineering department and municipal services department to find out what attributes were important to them so we could create these fields in our ArcPad forms. They told us what descriptions they wanted us to use and gave us condition assessment ratings for these features. This allowed us to build our ArcPad forms and create drop-down selections for each of the fields.
After we built the ArcPad forms for catch basins and manholes, we loaded them onto our pen-tablet PCs. We loaded the aerial photos of the city as well as our catch basin and manhole shape files. Then we hit the streets using our maps in ArcPad to start collecting the attribute data. We use Leica Geosystems GIS DataPro software to bring in our points collected with the rover and to upload points we want to relocate.
We found the program to be very easy to use. We just double-click on the symbol of a catch basin or manhole, and the appropriate form will pop up and tell what attributes need to be collected for that feature. We then fill in the blanks using the drop-down selections. This means the data collected is standardized. We then drop the data right into our ArcView 8.x database and ArcInfo software to manage the data in the office. We sometimes edit attribute data in Microsoft Access before dumping it into ArcView.
When collecting data on the manholes, we note barrel size, material and condition, and note all of the pipes in each manhole, recording their size, material, direction and depth from rim to pipe invert. On catch basins, we note the same common features plus grate type. We also note whether each catch basin is bike safe, whether there is a bike safety adapter on the grate and whether it has a gas trap in it. Recording data on the outfalls is simple. We usually just record pipe size and material, and if there is erosion control around it. We also note if it is a headwall, flared end section or just a straight pipe, and we take a photo of each feature.
GPS Expansion: Endless PossibilitiesThe GPS-based GIS system has expanded beyond the initial project of mapping manholes and catch basins. We have also used the GPS technology for doing as-builts of new construction to keep our database updated and to map the new impervious areas for our storm water billing. Without the GPS data, we would have had to wait until the next time we had aerials flown of the city (typically once every five years) to measure that new data or have an inspector measure the areas with a tape. With the GPS, we found we could map these areas and add them to our existing maps. This way we have accurate maps of where the buildings and parking lots are on the parcels. We also have started adding data being gathered by the sewer pipe video crews; in many cities, video crews are assigned to film the inside of sewers remotely by inserting cameras on long cables. The new system now allows us to work with consultants to do water sampling for our environmental impact studies on the Rock and Mississippi Rivers. The GPS data makes it easy to navigate back to areas where samples have been taken in order to take new samples for maintaining historical data.
The next step for utilizing our new system will be to map our water distribution system. We plan to buy a third rover for utility location crews to stakeout utilities that have already been mapped and to collect new features such as water service valves. We expect to use the system to capture data on all of the city's traffic signals, traffic signs, trees in the rights of way and any other city assets that can be mapped. There have even been discussions of using telemetry devices on city vehicles that will be tied in with the GPS to manage the fleet. This will allow them to keep track of data from our snowplows in the winter and to find the closest crew to a service call to help a citizen in need.
We have been getting excellent levels of accuracy with our GS50+ rovers. For quality control, we take periodic measurements against the HARN points in our area. Horizontal accuracies have been within 0.01 ft, depending on the satellite coverage on any given day. On average, we consistently see vertical accuracies of around 0.035 ft, which is very acceptable for our applications.
Sharing Data: Moline and Davenport Join InThe productivity gains in Rock Island helped persuade the cities of Moline and Davenport to allocate the funding to join us in a regional GPS consortium. We established an annual subscription fee that amortizes the capital investment for the base station and covers the ongoing maintenance and operating costs. Both cities bought their rovers from and were trained by our dealer, Turning Point Systems Group, who programmed their rovers to be on our frequency. Turning Point also programmed all of the systems to ensure data was received in the respective cities' coordinate systems, which are on two different coordinate planes. Moline and Rock Island are in the Illinois West region, while Davenport is in Iowa West.
The View from MolineJoe Morocco, GIS manager for the city of Moline, has reported that the city's experience with implementing the GPS has been very efficient. "The acquisition of the GPS technology and our partnership with the city of Rock Island have worked out extremely well. Partnering with Rock Island has allowed us to get up and running quickly, leveraging from their experience with the technology. It has also been a cost-effective solution, reducing the start-up capital required to get this project moving.
"GIS is being used throughout Moline. The water division is currently using it to streamline its records management. It also allows the staff members to see the dynamic relationships formed with other municipal services. Our engineering department is utilizing the GIS for design plans, storm water maintenance plans and records management. The addition of this technology has greatly reduced both the time and effort required to access information vital to our everyday duties."
The View from DavenportJerry Rodgers, survey supervisor for the city of Davenport, says, "We decided to purchase GPS to help us with our storm water management program. We are using it to map our storm sewers and storm water detention basin throughout the city. Some added benefits we have found are that we can use the GPS to set control for our new construction projects, and it is great for doing quick checks on possible elevation busts of a foot or more on questionable bench marks.
"During the slow times between projects, the city of Davenport's surveying crew uses the GPS to tie in section corners located throughout the city. This allows us to maintain accurate maps of all of the control within the city. We decided to sign on with the city of Rock Island to use its GPS base station after they approached us and explained how their base station already provided coverage for all of Davenport. This helped us realize the possible cost savings and the elimination of possible problems and delays of establishing our own base station."