The Use of Digital Orthophotos in Automated Mapping/Facilities Management Systems
Mr. Kirk Contrucci Manager, Photogrammetry Ayres Associates 2445 Darwin Road Madison, Wisconsin 53704 Tel: (608) 249-0471, Fax: (608) 249-2808 Mr. Ted J. Grillo Manager, Domestic Sales AGRA Baymont, Inc. 14100 58th Street North Clearwater, Florida 33760 Tel: (813) 539-1661, Fax: (813) 539-1749
Introduction
The integration of digital orthophotography with automated mapping/facilities management (AM/FM) systems has revolutionized how utilities collect and utilize accurate landbase data. For many years, utilities have used vector Iandbase maps as a component of an overall AM/FM system. Many of today’s modern AM/FM systems use high-resolution imagery as a backdrop to facility maps. This paper focuses on the integration and use of digital orthophotography in AM/FM systems. In the deregulated utility industry, companies require Iandbase mapping that is accurate and complete. The search is on for low cost mapping that can support detailed planning. Digital orthophotography meets these criteria. Until recently, however, utilities required large, powerful, expensive computer systems to manage and manipulate digital orthophotography and other high-resolution imagery. With the advent of powerful, low cost computer systems, digital orthophotos have become a viable alternative to traditional vector landbase maps in AM/FM systems. A digital orthophotograph is a geographically referenced high-resolution scan of an aerial photograph. The distortions caused by minor anomalies in the camera lens, relief on the earth’s surface, and tip and tilt of the airplane at the moment of exposure is removed through a rigorous mathematical process. The resulting gee-referenced image provides an excellent landbase map for AM/FM applications. As accurate as vector based maps, digital orthophotos provide the added benefit of being a much more complete source of information. Cost Benefits of Digital Orthophotography Held to the same accuracy standards as traditional vector based maps, photogrammetrically produced digital orthophotography costs less. This is especially important for those utilities whose areas of interest cover thousands of square miles in rural areas. In this age of increased competition in the utility industry, accurate, cost effective Iandbase solutions are vital to any utility’s success. Digital orthophotography provides the accuracy required for detailed AM/FM applications at less cost than traditional vector maps. It should be noted that, as with vector based maps, cost increases with accuracy. The key to determining the “right scale” is finding the right mix of accuracy, visible detail, and cost. Due to the high cost of vector based mapping, many utilities are reluctant to update their kmdbase maps. Less costly to create in the first place, digital orthophotos also have the advantage of being less costly to update than their vector predecessors. Unless major construction has occurred, the DTM surface created during the original orthophoto project can be reused, saving considerable project fees. Typically, the ground control information can also be reused in the update digital orthophoto project. These factors combined result in update project fees as much as fifty percent lower than traditional project costs. The compatibility of digital orthophotography into GIS and AM/FM systems provides another valuable benefit to utility companies. All the major GIS vendors have integrated raster handling capabilities within their systems. Until recently, GIS provided an excellent example of closed systems. The systems were designed and built from the ground up, with proprietary development tools and data management systems. Whh the very standard raster based file formats used for digital orthophotos, this potential pitfall can be avoided. The ease with which digital orthophotos can be integrated into AM/FM systems is another factor accounting for their recent popularity. Another major advantage of digital orthophotography is it provides a more complete source of information than vector based maps. Unlike photogrammetrically produced vector mapping, in which an operator interprets, then digitally captures landbase features through viewing the aerial photography, the scanned aerial image allows the user to interpret the Iandbase features for himself or herself. The clarity and detail visible on the digital orthophoto depends upon the scale of the aerial photograph used and the scanning rate employed. As flying height increases, accuracy and visible detail decreases. A 1”= 1,000’ digital orthophotograph of thirty-six square miles with a three foot pixel resolution will cost less but show less detail and be less accurate than a 1“=400’ digital orthophotograph of a four square mile area with a one and a half foot pixel resolution. Careful consideration should be given to the intended applications when determining the scale and resolution of the digital orthophoto Iandbase map. Michcon’s Mars Project a Case Study Michigan Consolidated Gas (MichCon) is Michigan’s largest natural gas company and one of the fastest growing diversified natural gas companies in the United States. With 1996 revenues of 1.23 billion and a total of 1.17 million customers from five hundred communities throughout the upper and lower peninsulas of Michigan, MichCon’s desire to provide top quality customer service resulted in the implementation of the Mapping and Automated Recordkeeping System (MARS). With accurate facility maps linked to ownership information, MichCon can readily access information that will serve its customers’ needs faster and more efficiently than previously thought possible. When the MARS project is complete, MichCon will be one the first utilities to use digital orthophotography for AM/FM applicaticms across most of its service territory. In 1995, MichCon searched for an alternative to the vector landbase maps they were currently producing. With more than fifteen thousand square miles of service territory to map, the traditional vector based map product was no longer a cost effective solution. Several factors pointed MichCon towards digital orthophotography. The company serves a large geographic area, with a wide range of customer density within its service territories. While vector based mapping provided an acceptable cost per customer alternative in downtown Detroit and Grand Rapids, the numbers simply did not add up when applied to the rural areas of Michigan. Through consultation with Ayres Associates and AGRA Baymont, Inc., MichCon determined that the benefits of digital orthophotography discussed above justified its use in these areas. In MichCon’s case, the digital orthophotography is produced from aerial photography flown at an altitude of fifieen thousand, eight hundred forty feet above mean terrain, which results in an aerial negative scale of 1“=2,640’. The photography is scanned at a rate of fifteen microns, creating a raster file approximately one hundred forty-four megabytes in size for each scanned photograph. Ground control points visible on the aerial photography are used to register the scanned photographs to a coordinate system and datum. Distortion on the photo due to relief is removed through first creating, then applying to the photograph, a digital terrain model (DTM) surface. Once the photograph has been rectified, 1“=400’ scale sheets are cut from it, with each sheet covering four PLSS sections. The file size of each 1“=400’ digital orthophoto is approximately fifty-nine megabytes. The flexibility, accuracy, and relatively small file size of MichCon’s digital orthophotos make them a valuable resource even before the full implementation of MARS. Like most utilities faced with the daunting task of scale correcting more than ten thousand inconsistent paper facilities maps for input into its AM/FM system, MichCon elected to outsource this responsibility to specialists. Ayres, supplier of the digital orthophotos, and Baymont, MichCon’s data conversion vendor, have worked together to take advantage of the benefits offered by digital orthophotography during conversion. Upon receipt of digital orthophotos from Ayres, Baymont adds intelligent cultural data to the landbase model. Database records containing street names, address ranges, railroad names, political boundaries, and other major landmark attributes (e.g., hospitals, schools, etc.) are linked to vector graphic features drawn over the digital orthophotos. These attributes are derived from a variety of sources including:
Once intelligence has been added to the orthophotos, they are displayed for use as a reference during facilities feature conversion, increasing the efllciency of this task. For instance, discrepancies on a client’s source records frequently require technicians to submit questions to the client for resolution. However, the presence of the orthophotos frequently enables technicians to resolve discrepancies that would normally require a field check on the spot. Following Iandbase and facilities conversion, Baymont delivers the data in the required format to MichCon along with the digital orthophotos. The completed model supports the spatial query functions normally associated with AM/FM systems while the orthophotos provide a level of visual detail unavailable in traditional vector-only models. MichCon’s MARS project also offers an example of how digital orthophotos can be integrated into existing AM/FM systems. In many of MichCon’s Northern Michigan service territories, which were converted prior to the decision to implement digital orthophotography, customer information is attributed to low accuracy vector maps produced from USGS quadrangles. While these vector maps provide the points and lines necessary for data attribution, the accuracy of the centerlines of roads, waterlines, and other landbase features is inappropriate for more detailed applications. In these instances, the digital orthophotos are used as backdrops in a process that scale corrects the existing vector landbase maps. By overlaying the low accuracy vector Iandbase maps on the high accuracy digital orthophotos, the vector maps can be quickly and easily corrected. This method saves the previous attribution of these features and results in final vector maps equal in accuracy to the backdrop digital orthophotos. Other Applications Digital orthophotos can be used in a wide range of AM/FM applications. A popular application for digital orthophotos in AM/FM systems is in corridor and site planning. Anyone who has dealt with landowners and right-of-way issues will tell you that accuracy is important when planning a pipeline location. With an accurate digital orthophoto, a planner can determine the most cost effective and least disruptive route for a potential pipeline. This is particularly important in cases where the landowner has provided only a narrow corridor for the pipeline location. Digital orthophotos are an excellent tool for locating and delineating wetlands and floodplains, helping the planner to avoid these environmentally sensitive areas. Environmental impacts are minimized and costs are reduced through effective right-of-way planning. Combine the digital orthophoto and its corresponding DTM and planners can identify the optimum route for pipelines or power lines based on terrain, which can certainly impact both the performance and cost of the proposed system. Companies installing miles of underground fiber optic cables reap big rewards by employing digital orthophotos to select the most efficient and least costly routes for network expansion. Wireless communications companies can use digital orthophotos and the associated DTM to determine optimum locations for personal communications system cells to maximize service coverage. As a planning tool in AM/FM systems, digital orthophotos simply outperform their vector based brethren. Effective facilities maintenance is a vital part of every utility’s business plan. Digital orthophotos provide a much broader range of applications in this area than traditional vector based maps. One example is right-of-way management. Many electric companies are now relying on digital orthophotography to monitor vegetation growth in right-of-way locations. By identi~ing dead and dying trees on the digital orthophotos, these companies can anticipate and react to the potential of damaged power lines and power outages. This can help identifi potential service interruptions before they occur, saving money and time by eliminating costly field inspections. Of equal concern is the encroachment of man-made features onto utility right-of-ways. Digital orthophotos are used to identifi newly built roads and buildings on existing right-of-ways that could interfere with service. Using digital orthophotos on laptop computers, field personnel can quickly locate the general geographic location of underground lines, saving both time and money. Emergency response is another important component of facilities maintenance plans. Natural disasters such as fires, earthquakes, hurricanes and floods can cause great damage to a utility company’s infrastructure. The low costs associated with updating digital orthophotography and the potential for repeatedly collected high-resolution satellite imagery allows utilities to compare its Iandbase prior to a disaster to imagery obtained after a disaster has occurred. Trouble spots can be identified more quickly and efficiently and crews can be dispatched to these locations. This ability to get services up and running quickly afler a natural disaster is yet another example of the benefits of digital orthophotography. Conclusion This paper has outlined the benefits of digital orthophotography over traditional vector based maps in AM/FM systems. With the recent market release of more powerful computer systems, reduced costs of increased disk storage, and the cross platform portability of digital orthophotography, more and more utility companies are turning to digital orthophotography for their landbase mapping needs. High-resolution digital orthophotos provide more complete, accurate, and comprehensive information than traditional vector based maps. They cost less to produce and update. They can be used for a variety of applications within an AM/FM system, particularly in service territory management and facilities management. The capabilities of digital orthophotography make them the logical choice for Iandbase mapping in modern AM/FM systems. | ||
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