Global Positioning System maps the way

The Ohio State University's Center for Mapping explores new applications for GPS technology

The GPSVan, a mobile data collection system that can map highway infrastructure
features while traveling at normal traffic speeds, exploits the commercial
potential of the Department of Defense NAVSTAR Global Positioning System (GPS).

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.

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