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

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.