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National Geodetic Survey

The Legacy of the Humble Bilby Tower

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Historic Traveling Bilby Tower 'Comes Home'

Innovative Survey Tower from Early 20th Century Returns to Indiana

two images of a Bilby tower under construction

Survey towers were used by U.S. Coast and Geodetic Survey surveyors from the mid-1800s through the 1980s to obtain the clear lines-of-sight needed to conduct the surveys that are the backbone of our nation's spatial reference framework. One of the most enduring and widely used types of towers was the Bilby Tower, designed by Jasper Bilby in 1926. Today, surveyors rely on the Global Positioning System to map the U.S. shoreline, determine land boundaries, and improve transportation and navigation safety.

Bilby Tower construction

The Bilby Tower is very fast to construct, which made it an ideal tool for rapid surveying throughout most of the 20th century. A trained crew of five, with the right equipment but no crane, could set four survey marks and construct both inner and outer towers in just one day.

Former and current employees of NOAA's National Geodetic Survey (NGS) recently volunteered their services in Osgood, Indiana, where the Surveyors Historical Society erected a historic Bilby Tower in Osgood Trail Park. Osgood is the hometown of Jasper Bilby, who invented the innovative survey tower in 1927.

The temporary steel Bilby Towers were easily erected, torn down, and rebuilt at the next survey station. This revolutionized geodetic surveying, which, at the time, relied on clear "lines of sight" to obtain accurate measurements between survey points. Another advantage of Bilby's steel tower design was its extreme cost-effectiveness. Surveyors could build four Bilby Towers for the same amount of money that it had cost to construct only one of the wooden towers previously in use.

A few years ago the historical society learned about an abandoned Bilby Tower in Louisiana, and received permission to disassemble the artifact and transport it to Osgood. NGS volunteers helped rebuild the tower, which now stands as a permanent monument to Jasper Bilby and his pioneering contribution to geodesy's evolution.