Now available to read/download, senseFly’s latest case study details how transportation-engineering firm, J.L. Patterson & Associates, Inc. (JLP) surveyed a 30-mile rail corridor using an eBee RTK. The result: “Phenomenal” data accuracy, the job completed in a quarter of the time terrestrial surveying would have taken, and at half the cost of using manned aerial services.
The California High-Speed Rail Authority is responsible for planning, designing, building and operating the first high-speed rail system in the United States. The authority selected a consortium of firms to perform environmental and preliminary engineering work for the Burbank-Los Angeles-Anaheim section of the route.
JLP was tasked with the engineering design work required to support the preparation of the Record of Decision/Notice of Determination (ROD/NOD) with a deadline of December 2017. This meant having preliminary engineering work completed by early 2016.
The targeted area was a corridor measuring 30 miles (48 km) long by 1,500 feet (457 m) wide, situated on an active railroad that can carry 100 trains a day. “Traditional surveying would have required lengthy permits to access the railroad right-of-way and constant interruptions due to train traffic,” explains Marc Cañas, JLP’s vice president. “The original plan was to use conventional aerial mapping, via a manned flight, however the mapping firm wanted eight to ten weeks to fly and process the data. Since our team didn’t have the luxury of time, we turned instead to the eBee RTK.”
Trial, plan, execute
JLP’s team used the drone’s provided flight planning software to set a 3.6 cm per pixel ground resolution. This figure was chosen to ensure a high-quality ortho aerial while staying below the 400 foot ATO maximum elevation set by the FAA.
To map the 61 square miles corridor, JLP’s three drone staff flew 41 flights. These missions captured 11,800 images, with an average flight time of 28 minutes and average flight altitude of 200 feet. “Each flight’s images took between two and three hours to process in Pix4Dmapper Pro. After several iterations we found that we could queue up five instances of Pix4D and process simultaneously,” Cañas notes.
The efficiency achieved by JLP’s first ever large-scale UAV project surpassed the team’s expectations. Cañas explains: “We surveyed a dense urban corridor in less than a month. Traditional surveying would have taken more than four times as long and had we used manned aircraft the cost would have been double.”
Traditional surveying would have taken more than four times as long and had we used manned aircraft the cost would have been double
Not to mention that the quality and accuracy of the data that the eBee RTK produced was, Cañas says, “phenomenal”. “We were able to collect ortho-rectified images at one and a half inches [3.8 cm] per pixel—twice the resolution of even the best manned aerial product— and the data models we produced show accuracies of down to one inch [2.5 cm] for both vertical and horizontal—the kind of accuracies you can only dream of with conventional aerial methods.”