Illinois Department of Transportation Survey from Terrestrial and Aerial Lidar
By James P. Peterson II, PE, PLS
The Illinois Department of Transportation (IDOT) is responsible for planning, construction and maintenance of the state’s extensive transportation network, including highways, bridges, airports, public transit, rail freight, and rail passenger systems, with an annual operating budget of approximately $5 billion. The Illinois Division of Highways, a division of IDOT, and its nine district offices are responsible for the design, construction, operation and maintenance of the state highway system, and the administration of the local roads and streets program.
Tight schedules and funding have forced IDOT to look for innovative ways to accomplish more with less. Mike Blumhoff, PLS, Chief of Surveys for District 2 in Dixon, Illinois, wanted to employ airborne and terrestrial LiDAR to complete and/or supplement his traditional topographic route surveys. IDOT’s design engineers have already adapted the utilization of airborne LiDAR data sets—now the organization wanted to implement terrestrial LiDAR to provide a survey much like a traditional route survey while making use of the rich data from a LiDAR collection. This required that the data set meet IDOT standards and be manageable in size to work in Microstation and Geopak environments.
IDOT uses Microstation and Geopak to control standard design and surveying. Terrestrial LiDAR data can be very cumbersome in a typical CAD environment as these data sets can contain as many as 4,000 points per square meter. In addition, IDOT policies and procedures require strict adherence to department CAD and survey standards, and specific levels and cells are required for annotation. The definition of survey field codes requires an understanding of Geopak survey chains and contouring methods to generate an acceptable topographic base map with contours.
Sanborn proposed an IDOT-specific terrestrial LiDAR collection using static and mobile methods. Sanborn uses Trimble GX Advanced for static collection and Applanix Landmark for mobile collection, and merges imagery and LiDAR data for a complete terrestrial solution. Sanborn worked closely with Applanix and Trimble on a custom workflow and set of specifications that met IDOT’s requirements. The result was a unique solution for IDOT that included a combination of traditional survey, terrestrial LiDAR, airborne LiDAR, terrestrial photogrammetry, and a custom workflow. Louis Nastro, Director of Land Products for Applanix said, “Sanborn is doing something no one else is doing by creating a custom workflow that exploits the extraction of roadway assets, survey features, and 3D images from terrestrial and airborne LiDAR.”
IDOT proposed a pilot project in Jo Daviess County that included approximately one mile of U.S. Highway 20. The culverts on the site needed to be replaced while the main line of U.S. 20 East had to be relocated adjacent to U.S. 20 West.
The project presented limited right-of-way access and hazardous conditions, as a rock bluff on the north side and a steep slope on the south side made access to the site unsafe. Previously, airborne LiDAR was used to collect data from the site. The goal of the pilot was a Sanborn terrestrial LiDAR data collection to combine with the existing airborne LiDAR data to produce a Microstation/Geopak survey deliverable. The project control was provided by IDOT, and Sanborn provided the terrestrial LiDAR survey with custom workflows.
Sanborn performed a terrestrial LiDAR scan and image collection. Survey control was placed during the scan or at specific identifiable locations after the scan. The survey control allowed the LiDAR point cloud to be registered to the survey control, which provided absolute accuracies better than 0.10 feet for mobile mapping and 0.02 feet for static collection. The point cloud was then filtered to bare earth and non-terrain points were removed. Non-terrain points can be used to identify topographic features, but are not used for the bare earth surface.
Virtual survey points were selected in the image. Their positional accuracy was determined by the LiDAR data within the image, which provided survey-coded points and enhanced breaklines. Edge detection and breaklines are very important to proper surface generation because of the random sampling of a LiDAR collection. Sanborn’s custom workflow created the valuable 3D entities. From this virtual survey, the proper Geopak chaining of linework and breaklines was created.
A preliminary contour map was created that extracted specific key points—these specific key points were then used to generate contours very similar to contours created from the millions of points available. Extracting specific key points reduces the number of needed points to approximately 10% to 25% of the total available number of points. The key points are then combined with the virtual survey points and linework to form a complete Geopak surface. The terrestrial surface is then combined with the airborne LiDAR to create a complete surface for a large area.
As a result of Sanborn’s unique approach, IDOT benefited from a rich final product that was collected via safe and rapid methods. The collection was safer because necessary traffic lane access was reduced and/or eliminated, and the collection rate was faster than traditional surveying (traditional methods were still used for items that were limited from sight, for establishing control, and for quality control). The final product contained LiDAR data, 3D images, survey data, and manageable surfaces. Most importantly, IDOT received a complete LiDAR data set that can be used for alternate feature and class extraction.
Jim Peterson is vice president and assistant general manager for Sanborn’s Imagery Services Central division located in St. Louis, Missouri. Mr. Peterson focuses on business development for terrestrial LiDAR and cadastral GPS/GNSS surveys. Prior to joining Sanborn, Mr. Peterson was CEO of his own surveying and engineering company. Mr. Peterson is an adjunct professor of surveying and is a member of the academic advisory board of Southern Illinois University at Edwardsville.
For more information about Sanborn’s Terrestrial LiDAR/Mobile Mapping Services, please contact Mr. Peterson at email@example.com
» Back to our Aerial Mapping March 2009 Issue