Crossing into the Digital World

October 2, 2003
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Scanning Technology offers Mississippi DOT a safer way to do risky railroad crossing surveys.

The Mississippi DOT truck-mounted Riegl USA LMS-Z360 scanner utilizes “stop-and-go” scanning techniques to reduce field time by quickly taking multiple scans of a project that will later be merged in image post processing.


Dwayne Hollins safely initiates scanner operation from inside a Ford Explorer scan vehicle. He can configure the scanner and compile project data on the scanner’s laptop PC.
When the task before you and your group is to record the best possible data on more than 2,700 railroad crossings, you immediately begin to consider the most efficient means of technology possible. The Mississippi Department of Transportation (MDOT) Rails Division was presented with such a project a few months ago. MDOT staff members know that obtaining documentation of the state’s railroad crossings can be quite challenging, a task that warrants better technology than what the Division had in its arsenal. And the need for accurate, detailed information on railroad crossings is constant, as it is a major resource for the public, who often call to report accidents or dangerous conditions that have arisen. In order to address such calls, MDOT representatives need to be aware of previous conditions such as the type of signal installation, road striping and other warning devices. But, gathering such data can be risky and time-consuming.

In the past, the MDOT Rails Division had collected digital photographs of its railroad crossings, most of which are quite dangerous to work near. These photographs were then filed with hard copy reports. When a call came in regarding a certain crossing, Johnny Taylor, the coordinator for the Rails Division had to decipher the caller’s description of the crossing and retrieve the accompanying file, but often had to return the call. In addition to being time consuming, the process netted little data other than photos of poor resolution.

MDOT wanted to move into the digital age, offer more and better data, and be able to provide it in a database that was easily accessible for faster recovery. MDOT Senior Engineering Certified Technician, Dwayne Hollins was tasked to look into the possibilities of adding 3D laser scanning technology.

By using a truck-mounted 3D scanner, the Mississippi DOT increases worker safety and decreases the overall project impact to moving traffic. The field team can take scans without closing lanes or otherwise obstructing traffic.

Testing the Technology

Hollins led the effort to test 3D scanning technology and implement this valuable tool within the agency. With an ever-shrinking workforce and ever-increasing workload, MDOT management encourages innovative ideas to stretch taxpayer dollars. A railroad crossing test was the perfect venture.

To be implemented, the scanning technology needed to meet a series of MDOT quality and service objectives that include improving time management, customer service and project accuracy, and ensuring employee safety. When researching agency technology requirements, the survey equipment committee consisting of the district surveyors from the six transportation districts across the state considered these objectives during each phase of the review. After meeting with several 3D scanner vendors and testing equipment in actual field conditions, they concluded that the procurement of a 3D scanner would satisfy the MDOT objectives.

MDOT eventually chose the Riegl USA LMS-Z360 (Riegl USA Inc., Orlando, Fla.) scanner with InnovMetric PolyWorks data processing software (InnovMetric Software Inc., Sainte-Foy, Quebec, Canada). The Z360’s capabilities allow MDOT to use it in a variety of configurations. Riegl USA Inc. could also supply the technical support and equipment options designed specifically for the transportation surveyor.

Testing of the Z360 in actual field conditions included scanning of two railroad crossings in Jackson, and then comparing the LiDAR scanning with simple conventional methods for collecting pertinent data and digital photographs. One four-minute, 360-degree scan and two two-minute “approach” scans were taken at each crossing. An approach scan includes using a scanner that is mounted on a truck roof on the road surface 40 to 50 ft from the railroad intersection. Actual scanning time at each site was less than 10 minutes. In a few seconds, the raw data was saved in three formats named according to the MDOT railroad crossing number: a color JPEG, an intensity JPEG and the native Riegl 3DD file, the proprietary file name used in Riegl’s RiScan software.

MDOT further utilized the LMS-Z360 just north of Jackson in Madison County. This county was chosen as a pilot project due to its large size and the diversity of the subject crossings, which include urban, industrial and rural railroad crossings. Acting as a one-man survey crew, Hollins successfully obtained data for 31 crossings for a total of 93 scans in less than three and a half days. This included mobilization and travel between the multiple railroad company lines.

In addition to the detailed data they obtained in these short periods, MDOT staff realized they could meet the MDOT objectives of time management, employee safety, project accuracy and customer service.

Photogrammetric and LiDAR data captured by the scanner provides a 360 degree scanning radius ideal for minimizing the number of scans in a project and reducing field time.

Time Management

From the pilot test on the railroad crossings, MDOT officials realized that a railroad crossing could be scanned in less time than a railroad inspector could safely park and walk around the site. What’s more, current Geographic Information System (GIS) data linked to the 3D scanner data would provide a wealth of information over the previous railroad crossing procedures.

The MDOT crew decided that results from the Z360 come from its impressive speed and accuracy features. The scanner combines fast, accurate data acquisition with a large 360 x 90 degree field of view. These performance features make it practical to mount the scanner on the roof of a vehicle for efficient scanning. MDOT staff used a custom designed mounting platform offered by Riegl USA to mount the Z360 to a standard Ford Expedition truck. Generally, MDOT workers mount the scanner on the platform upon arrival at the jobsite and it remains mounted as the vehicle is driven from one scan location to the next. This “stop-and-go” method greatly increases field productivity by greatly decreasing setup time for each scan. Furthermore, the scanner is mounted on a swivel platform, making it easy to rotate 90 degrees for scanning unusual areas, such as the underside of an overpass. The roof-mounted scanner adds favorable height to the scan angles. The operator simply initiates each new scan from the comfort and safety of the vehicle. An optional lightweight aluminum cover can be quickly locked down over the scanner platform, providing protection against the elements.

While the scanner is in operation, the driver/operator remains still. Currently, MDOT surveyors scan targets at various scan angles and mesh them in InnovMetric’s PolyWorks post-processing software. Using a Magellan Meridian Gold WAAS-enabled GPS handheld (Thales Navigation Inc., Santa Clara, Calif.), the surveyor creates a feature within each scan and associates this with the raw 3DD data for approximate location and archival purposes. By mounting Leica Geosystems’ (Atlanta, Ga.) AT502 RTK GPS antenna above the scanner on a standard provided mount, a district survey crew can scan control points into the point cloud, reducing post-processing time.

The scanner can also be tripod-mounted and supplied power by 12-volt jumper/batteries. The system becomes a mobile, one-person survey crew, capable of collecting multiple data at multiple scan angles with very little setup time.

Riegl RiScan Pro control software uses a project-oriented user interface for scanner configuration and data organization.

Employee Safety

Unlike traditional surveying methods that may require survey crews to be placed in congested traffic areas or to snarl traffic with lane closings, the MDOT configuration of 3D laser scanning and “stop-and-go” implementation requires only one operator and doesn’t require the operator to be in the road or on the railroad itself to take the scan.

“Another interesting result of using the scanner is that moving cars and pedestrians are not a hindrance and can easily be removed during post-process clean up,” Hollins says. “A one-man crew can safely make successful roadside scans in busy traffic.”

This is right in line with MDOT’s objective to ensure public and employee safety.

Project Accuracy

MDOT’s old method of collecting digital photographs of the crossings netted very little usable data. After using the Z360 in the field, the scanned data files were downloaded to the public GIS server GeoMedia, a product of Intergraph Inc. (Huntsville, Ala.). A “workspace” was prepared and within a few moments three new “features” for each crossing were created. Filling in pertinent data, such as date, crossing number, street, city, county and MDOT district, then creating a hyperlink to the raw files took less than five minutes each. Total office time was about 15 minutes per crossing. The publicly accessible server only requires the user to download Riegl’s 3D RiView software to view the native 3DD files.

With just a few clicks of the mouse, any GIS employee from MDOT can zoom in on a crossing, click the feature and then choose how they wish to view the site—in color, intensity or in 3D—side by side with the 1 meter resolution aerial photograph, native to the system. The 5 mm accuracy of the scan images and various viewing perspectives allows MDOT to supply volumes of information needed by public and private entities.

Better Customer Service

The results of 3D scanning implementation by the MDOT Rails Division have been rewarding for the state agency as well as public and private users of this data. Not only does the agency now have more detailed information on the railroad crossings, but eventually all the railroad crossing scan data will be available on the GIS server. By setting up public GIS archives of this valuable railroad data, MDOT is speeding the information pipeline while also freeing up MDOT employee time for other responsibilities.

Undaunted About the Future

With testing completed—and proven—MDOT’s surveying staff plans to use the Riegl LMS-Z360 unit, with confidence, on the 2,700 crossing project while developing additional uses for scanner technology in other areas of the department.

This innovative use of Riegl’s “stop-and-go” 3D technology by MDOT is a clear example of hard-working DOT managers grappling with day-to-day issues and emerging with solutions that are cost-effective and enhance productivity while improving the safety of the traveling public. With the scanning solution, the 2,700-plus Mississippi railroad crossing project facing MDOT is no longer a seemingly daunting and challenging task. And anyone needing detailed information about the crossings, including GIS data, will be able to obtain it quickly.

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