Railway Track & Structures - February 2008 - (Page 31) Mapping Mapping using GIS, LiDAR and surveying As railroads look to increase capacity, they are considering changes to the rightsof-way, which call for more sophisticated mapping tools such as LiDAR. I n California, BNSF is in the process of adding second and third main line track in some of its right-ofway to help increase the capacity of its rail network. Other railways are looking to widen their rail corridors so they can straighten out curves. All of these planned and proposed right-of-way changes have prompted resurgence in the mapping of railroads. In the past year, Merrick & Company, an architecture, engineering and geospatial solutions firm based in Aurora, Colo., received two mapping contracts from railroad companies, both specifying the use of LIght Detection and Ranging (LiDAR). Airborne LiDAR data collection employs a scanning laser rangefinder to produce accurate topographic surveys. “Characterized by hundreds of miles of narrow linear corridors that cross multiple state plane coordinate zones, these railroad projects necessitated differences in approach, planning and implementation compared to the surveying and cartographic activities typically applied in large-area mapping projects,” said Yaneev Golombek, GIS specialist with Merrick. In 2006, BNSF contracted Merrick to provide surveying, LiDAR data acquisition, digital orthophotography, digital terrain models and GIS-ready files for a 453-mile section of track between Barstow and Oakland, Calif. The railway was eyeing this busy segment for capacity expansion. “We wanted to be proactive in having the engineering information available when we release proposal requests for construction,” said John Fleming, BNSF manager of engineering and construction. “The BNSF project typifies the challenges of mapping a railway corridor,” said Bill Emison of Merrick. “Project specifications called for the acquisition of LiDAR elevation data with a twofoot ground sample distance suitable for generating one-foot contours. Digital orthophotography was required to be collected at 0.25-foot ground resolution for planimetric mapping that would meet or exceed ASPRS accuracy standards for 1-inch=100-feet mapping. All created files were to be delivered in MicroStation format.” From a purely technical standpoint, the specifications were well within the standard operating parameters of the Merrick airborne data collection systems. The company operates its own Digital Airborne Camera System designed to acquire extremely-high-resolution color imagery simultaneously with elevation data from a Leica ALS50-II airborne LiDAR sensor. Both the camera and the LiDAR sensor are integrated with an airborne GPS system and an inertial measurement unit, which tracks the plane’s attitude in flight. “Although technical difficulties would be faced and overcome, we viewed coordination among the three distinct phases of this project as the most important challenge,” Emison noted. “These phases–Surveying, LiDAR Acquisition and GIS Integration–were managed as fullyinter-related activities that required joint planning and implementation by the appropriate technical teams within Merrick. Participants agree this integrated approach was crucial to the overall success of the project.” Surveying ground control “Merrick maintains its own survey BNSF turned to sophisticaed mapping methods to obtain needed right-of-way data for capacity expansion measures. Railway Track & Structures February 2008 31 www.rtands.com http://www.rtands.com
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