Riding the Rails with Mobile Scanning

The North Carolina Railroad Company (NCRR) built its railroad in the 1850s, with a 200-ft. boundary corridor extending 100 feet on either side of the rail centerline. Today, the track spans 317 miles and carries 50-60 freight trains and 10 passenger trains daily. Development has significantly encroached upon the original corridor.

NCRR needed a much better idea of where our original centerline and corridor boundary lie, said Kristian Forslin, GISP, GIS coordinator with NCRR. Having this information allows NCRR to better manage our corridor, as well as provide a firm basis for future rail engineering projects.

NCRR first tried a GPS mobile solution by others to collect the data. Our initial test with the GPS approach presented a level for potential failure in a number of areas that NCRR was not willing to accept, said Forslin. At that point, NCRR decided to pursue mobile scanning. Mobile scanning technology promised to be far superior based on speed, reliability and its thoroughness in one pass, he said.

NCRR commissioned the Raleigh, North Carolina-based firm of McKim & Creed to collect accurate existing rail centerline locations and produce coordinate geometry of all tangents, curves, spirals, etc., of those centerlines.

Mounting and Calibrating the System

McKim & Creeds MoDaC Mobile Data Collection system utilizes two GPS units, an inertial measurement unit (IMU) and a distance measurement instrument (DMI) that work in concert with two LiDAR sensors and three digital cameras to collect survey-grade accurate positional data. We mounted the system on NCRRs hi-rail vehicle. Once the system was mounted, we rechecked the calibration by scanning a nearby building, and made the necessary dimension adjustments between the DMI and IMU units.

Mission Planning and Coordination

Along several areas of the track, tree canopy limited the GPS sky view to satellites. The team scheduled data collection during optimum GPS conditions when the most satellites and the best geometric positioning were available. The IMU and DMI units on the MoDaC system helped tremendously when GPS signals were temporarily lost or blocked. We coordinated the optimum GPS conditions with available track time to avoid interfering with the train schedules.


All personnel who accessed the property were certified in both e-Rail Safe and Roadway Worker Protection (RWP). Surveyors collected data primarily from inside NCRRs hi-rail vehicle, accompanied at all times by representatives from both NCRR and Norfolk Southern.

Ground Truthing

NCRR needed accuracies within a 0.10-ft. tolerance. To ensure this accuracy, McKim & Creed conducted ground truthing conventional surveys at approximately -mile increments along the corridor. We located existing pavement markings near at-grade crossings such as stop bars and edge of travel-way lines. Temporary v-shaped targets were set and controlled in areas where pavement markings were not present. All ground truthing points were obtained using RTK-VRS collection from the North Carolina Geodetic Surveys (NCGS) network while avoiding fouling the tracks. These points were used to adjust our LiDAR data to achieve the required accuracies, especially in the poor GPS areas that were impaired by blockages.

Processing the Data

The data was initially processed to a Universal Transverse Mercator (UTM) coordinate base, which ensured that all scan data, GPS data and imagery were collected accurately and thoroughly. Once the raw data was processed, it was computed horizontally to the North Carolina State Plane Coordinate System, NAD 83 and vertically to the North American Vertical Datum (NAVD88). Various best-fit computation routines were incorporated to provide true geometry of the alignments. McKim & Creed delivered our best-fit compilation of the existing track centerline geometry for the entire 317 miles in MicroStation, ArcGIS and GEOPAK formats to be used by the surveying community for future right-of-way monumentation needs.

Additional deliverables included dual imagery as the project was scanned and a forward-facing completed video. McKim & Creed also created a KMZ file that opens Google Earth, zooms into the geographic location of the route, and displays photos of that particular location.

Whats Happening with the Data

NCRR is using the data to support monumentation of the corridor boundary. When that is complete, NCRR will fine-tune its GIS with the newly acquired centerline data and monument locations.

Although a full-blown LiDAR data acquisition deployment may be seen as overkill for our project, it was the best way to quickly get the accurate centerline data NCRR needed, Forslin said. This information will be a great asset to surveyors who will have a significant amount of new control to choose from, as well as a reduced need to obtain right-of-entry permits for work adjacent to the corridor.

Tim Van Gelder, PLS, is a regional manager with McKim & Creed and oversees the mobile scanning activities of the company. McKim & Creed is an engineering, surveying and planning firm with 350 employees located in offices throughout the South. In May, the company was named the largest surveying and mapping company in the Southeast by ENR Southeast magazine. McKim & Creed has also been ranked one of the top architectural/engineering/contracting firms by Public Works magazine, and one of the top 500 design firms in the United States by Engineering News-Record magazine. More information is available at www.mckimcreed.com.

The North Carolina Railroad Company owns and manages the 317-mile rail corridor extending from the Morehead City Port to Charlotte. NCRR is the oldest private company in North Carolina and remains at the forefront of rail improvements and partnership development to promote jobs and rail-served industry across the state. More information is available at www.ncrr.com.

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