Global Positioning System maps the way

By: David Banasiak

It successfully surveyed 1,000 miles of roadway in Clark County, Ohio. The project, jointly funded by Ohio DOT and the county engineer's office, recorded 15,000 features along the side of the road. Three video cameras-mounted on the front, side and rear of the van-produced a high-resolution photographic log of the work.

The van includes a satellite receiving station that can determine the vehicle's geographic position using the GPS system in differential mode. It also uses an independent dead reckoning (DR) system to record positions when satellite signals are temporarily lost due to overhead obstructions. An operator can add attribute and text information by using a PC keyboard or a touch screen.

An analog Super VHS camera system runs in continuous video mode, capturing a photographic log of the survey. Each video frame is time tagged to the GPS signal and a geodetic coordinate is assigned to each image. This imagery provides valuable information for urban planners and delivery and transportation industries.

As the GPSVan moves along the roadway, a digital stereo camera system records stereo images of features. Using this imagery, coordinate positions (i.e., latitude, longitude and elevation) of objects such as road edges and centerlines, curbs, and mile markers can be recorded. These objects can be measured photogrammetrically with a precision of 5­p;10 cm for features located within 10­p;40 m of the van.

Data from the GPSVan can be converted into a format acceptable for entry into a Geographic Information System (GIS). After the information is analyzed, it can be used to monitor road and transportation features, establish management priorities or develop other databases.

Last year, the GPSVan technology passed rigorous production tests. The technology successfully operated in a production environment, mapping railroad infrastructure.

Over 6,000 miles of Burlington Northern Railroad (BNR) line were surveyed by General Railway Signal Corporation and TRANSMAP Corp. Nearly all the features required by BNR were located within a few tens of centimeters. The project involved processing 500,000 stereo image pairs through its stereo image-processing system.

StereoMap post-processing software was use to deal with the large volumes of stereo imagery generated. Use of StereoMap in a production-mode was quite different from earlier sporadic and limited data processing.

The extended use of StereoMap revealed a number of implementation inefficiencies that have been analyzed and corrected. Hundreds of thousands of stereo image pairs have been processed with feature coordinate accuracy well in the sub-meter range.

The Ohio State University Center for Mapping (the Center), Columbus, in collaboration with industry partners, enhanced the GPSVan system's data reduction and processing software throughout the year. In addition to Stereo Vision and GPS/DR software enhancements, the video post-processing software was completely rewritten. This improved both the quality of the data collected by the system and the productivity of post-processing operations.

In response to field survey demand to increase data acquisition speed, several tests were conducted to identify potential improvements. Turning to the hardware compression on the 8mm digital tape system has shown some improvement in speed and revealed that the speed of the signal-processing subsystem should be increased to fully realize the faster data transfer rate offered by the hardware compression. A faster signal-processing CPU and a double speed control CPU were installed in the fall, resulting in a 20% increase in performance. In practical terms, the GPSVan can now collect stereo image pairs in 100 ft intervals while traveling at 55 mph.

The GPSVan technology has been successfully demonstrated in operational environments-surveying roadways and railroads-and the data acquisition and data processing software continue to be enhanced. New video post-processing software has been completed, and a new stereo vision module is under development.

This six-year project demonstrates the difficulty of commercializing a new technology, especially one that challenges the status quo.

Nonetheless, a revolutionary mapping system has been brought from concept to full commercialization in a highly successful manner. In addition, four companies, employing over 20 scientists and technicians, have been created to commercialize this technology. The Center and its industry partners plan to continue to invest in imaging technology development.