The Use of Digital Orthophotos in Automated Mapping/Facilities Management Systems
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.
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