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GPS Utility Inventory.

Conducting a GPS utility inventory as the first step in developing a comprehensive infrastructure GIS requires more effort than simply reading a GPS manual, operating equipment, and collecting points. Doing it right the first time means asking questions up front, defining the project parameters, and then evaluating all the options before making decisions that will shape the accuracy, completeness, quality, and usability of the final product.

SAGIS (Savannah Area Geographic Information System)-- a consortium of the city of Savannah, Chatham County, Chatham County-Savannah Metropolitan Planning Commission, and Savannah Electric-- knew that the city of Savannah's GPS inventory of water, sanitary, and stormwater structures had to be planned in detail. If not, the city's investment of $2.2 million in GIS infrastructure, being developed by Woolpert LLP (Dayton, Ohio), would not meet the city's need for facility maintenance and management; data maintenance; utility system expansion and inventory; water quality analysis; and capital improvement planning and budgeting. So SAGIS and the city insisted upon a comprehensive planning effort long before GPS field crews located the first structure.

Planning effort 1. An in-the-field GPS workshop, called a test drive, was conducted to confirm the project approach and uncover hidden issues to be addressed.

A test drive would allow SAGIS/Savannah participants to see firsthand how the inventory would be performed and what technology would be needed so budget and schedule could reflect actual procedures to be used. Two GPS methods were being considered: real-time differential (RTD) GPS, which provides horizontal accuracies of two to three ft for mapping and planning applications, and realtime kinematic (RTK) GPS, which provides horizontal and vertical accuracies of three to five centimeters for engineering applications. Test drive results confirmed that RTK GPS was not feasible, and SAGIS/Savannah participants in the field saw why: the area's dense tree canopy made only 35 percent of structures GPS-observable with RTK. A second sweep with a total station would have been required to obtain three to five centimeter accuracies on these structures--thus making RTK GPS inefficient, time consuming, and costly. RTD GPS was adopted instead since the test drive showed that 75 percent or more structures would be GPS-observ able with this method.

During the test drive, the Woolpert crew not only tested GPS survey methods and collected structure locations but also popped manhole lids, logged attribute data into a hand-held pen-based PC, and began building network connectivity. SAGIS/Savannah observers asked questions such as:

* What attributes do we really need for each located feature?

* If a structure is difficult to find, how much time should the GPS crew spend looking for that feature?

* What happens if the GPS crew cannot find a structure?

After the test drive, SAGIS/Savannah and Woolpert better understood the level of effort required to locate structures: debris or sediment in the field can mask a valve clearly outlined on a source document; unless the street is swept, the valve may not be found. Sometimes structures were difficult--if not impossible--to find because they had been buried, paved over, or hidden by landscaping. In these cases, Woolpert crews would have to use metal detectors to try and locate the structures.

As is typical in areas with older utility systems, manhole covers labeled "STORM" occasionally revealed part of the sewer system; a few underground pipes led to nowhere; and some structures simply could not be found in the field at all. The test drive showed that city crews for water, sanitary sewer, and stormwater would need to commit significant time to help locate features in the field. (Other local governments considering a similar project should recognize that this time is substantial and should be considered when developing field crew work plans.)

Test drive results let SAGIS/Savannah refine the scope of work, determine the final list of structures and attributes to be collected during the inventory, and address questions before they became show-stoppers in the field:

* If a point is not GPS-observable, how will the feature be accurately placed in the GIS? Resolution: Features will be recorded in the database as either "GPSed," "Obscured," "Inaccessible," or "Not Found." City crews will go into the field, attempting to locate all "Not Found" features. Once these locations are reported, Woolpert will then return to the field to obtain the positions and fully attribute these GPS points. (The test drive also confirmed the need for the city to gather any and all source documents available so GPS field crews had sufficient information for finding structures; this would help minimize the number of structures deemed "Not Found" by GPS field crews.)

* Since condition ratings are subjective--a condition judged "good" by one person may be rated "poor" by another--can they be standardized? Resolution: If a structure is functional, its condition will be considered acceptable (and recorded with a "0" in the database); if a structure is not functional, its condition will be considered unacceptable (and recorded with a "1" in the database). This convention lets city crews quickly identify structures needing repair. GPS field crews notify the city immediately if they discover severe or dangerous conditions such as clogged pipes, missing or broken manhole covers, or leaking manholes. Thus, the inventory serves as an overall utility system inspection and evaluation of sorts since city crews can immediately address problems they otherwise might not have known existed.

* If a structure is difficult to find, how much time should the GPS field crew spend looking for that feature? Resolution: GPS field crews will visually scan for a structure for up to two minutes. If the structure cannot be found, the operator in the field will digitize its relative position on the pen-based computer's planimetric map and note the feature's "Not Found" status.

Planning effort 2. A detailed field procedures manual was developed that outlined the step-by-step guidelines for collecting data and obtaining system connectivity in the field.

The manual was the project's primary planning tool and outlines exactly which features to collect and how to collect them based on test drive results. For example, city staff noted that underdrains should be captured but laterals should not, and that only the presence of an independent valve, not its precise location in relationship to a hydrant, should be noted. If procedures such as these had not been identified upfront, GPS field crews might have spent time getting positional information the city did not need. Moreover, if changes had to be made midstream, then collected data would have to be modified, causing delays, second sweeps, and higher costs. The manual covers hundreds of issues such as:

* How should the public be notified before GPS work begins in an area?

* What uniforms will GPS field crews wear?

* What precautions should GPS field crews use in high traffic areas?

* What source documents will be available on the pen-based PC for use during field data collection?

* What are the data collection processes specific to water structures? Storm? Sewer?

* What is the inventory procedure for structures on the edges of map sheets?

* How should a structure be identified in the field once it has been inventoried?

* What will be covered during weekly meetings?

While documenting procedures, the team identified issues that would not have come up until much later such as, "How should we attach attributes, on the fly and in the field, to pipes that have not yet been mapped?" and "How can we be sure we are not collecting data on a private utility system?"

The manual also addressed potential errors of interpretation related to structure names as revealed during the test drive. To bridge the guage gap, Woolpert determined that photos of each structure types would be taken and reproduced in the manual with the appropriate labels, along with sample construction drawings, so that only references familiar to city users would be incorporated into the database.

While most issues were addressed early, some issues could not have been foreseen and had to be addressed as the project evolved. For example, city staff were surprised to learn that more features than expected were difficult to find in the field; as a result, the city has dedicated additional field crews to find structures that may have been buried, paved over, or hidden by landscaping. (A side benefit: because the inventory is revealing "new" structures previously inaccessible, city maintenance crews can respond to emergencies and service calls faster and more efficiently.)

Weekly meetings, required since the beginning of the project, ensure the plan is being followed, guarantee that concerns are addressed immediately before they slow inventory progress, allow Woolpert and city crews to exchange information about "Not Found" structures, and keep the quality control process on track.


Thanks to comprehensive, hands-on planning and testing, concerns were resolved and standard processes established before time and money were spent building the overall system. SAGIS/Savannah participants, who have remained involved in every phase of the project, now have an insider's view of how GPS data is being collected and how the GIS is being developed--step by step.

Mr. Cestnick is Project Manager with the Miami, Florida office of Woolpert LLP Dayton, Ohio, and Mr. Locke is Systems Analyst, Information Services Department, city of Savannah, Georgia, and Project Manager of the SAGIS Utility Conversion Project.

Statement 34

More municipalities are expected to begin utility inventories now that Statement 34, issued in 1999 by the Governmental Accounting Standards Board (GASB), is in effect. The mandate requires governments to report financial information about all their capital assets, including public infrastructure assets. To begin meeting Statement 34 requirements, municipalities must have updated information about their infrastructure. GPS will be the method of choice for municipalities that want to begin with an accurate, up-to-date inventory and condition assessment of their utilities. Municipalities should plan GPS utility inventories not only to help meet the financial reporting requirements of Statement 34 but also to provide an accurate, complete, and solid foundation for additional applications.
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Title Annotation:Savannah Area Geographic Information System
Author:Cestnick, John; Locke, John
Publication:Public Works
Geographic Code:1U5GA
Date:Nov 1, 2000

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