The mission of Ohio's Department of Transportation (ODOT) is to seamlessly link Ohio's highways, railways, transit systems, aviation and port facilities to promote an efficient, cost-effective and reliable multi-modal transportation system. To this end, ODOT performs extensive planimetric and topographic mapping as part of the necessary planning and design associated with highway improvement projects.
ODOT's past practice for mapping of this kind was the traditional film-based approach (Digital Elevation Models for orthophoto generation, orthophotos for planimetric mapping, stereo imagery used for topographic mapping, ground survey, etc.). This traditional approach yielded good results but was very time consuming and costly.
"Bottlenecks" in the process meant critical projects were delayed and costs increased. ODOT needed to remove the "bottlenecks" to reduce the time, number of resources, and ultimately the cost of highway planning.
A three-step solution was implemented:
Step#1: Enable Direct Georeferencing of the Film Camera
ODOT added an Applanix POS AV 510 GPS/INS system to its LMK large format film camera, allowing for direct georeferencing of the camera. Having the direct Exterior Orientation (E.O.) provided by the POS was a significant improvement as it allowed for a large reduction in ground control as well as a check against the AT (aero triangulation) solution. Step 1 resulted in a significant reduction in turn-around time, cost, and re-work for ODOT.
Step#2: Implement Airborne LIDAR
Seeking further productivity gains in 2004, ODOT purchased an ALTM LIDAR from Optech integrated with the Applanix Digital Sensor System (DSS). By utilizing LIDAR, ODOT was able to increase vertical accuracy and speed in the generation of Digital Elevation Models (DEMs), while simultaneously reducing costs and time. Other benefits realized include:
- More accurate ground elevations in forested and vegetation covered areas
- More dense pulse footprint (point spacing)
- Automated, efficient, and cost-effective data post-processing
- Lower cost per acre surveyed
Step 2 resulted in a significant improvement in the topographic mapping process and an accelerated rate of orthophoto production.
Step#3: The Applanix DSS + LIDAR Solution
Up until this point the DSS system was used only for LIDAR data editing purposes. Now a medium format 16 MP digital camera (DSS) provides imagery collected simultaneously with LIDAR to create orthophotos for planimetric mapping. Using digital images eliminated the need for film development, annotation, scanning, and the correlation of scanned images to E.O. data. The GPS/INS solution for the digital images and the LIDAR data fit together seamlessly for very rapid orthophoto generation.
The End Result
The DSS with LIDAR solution enabled the simultaneous collection of the digital images with LIDAR and yielded excellent accuracy. ODOT realized huge savings in time and cost.