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Maricopa County, AZ
Thanks to an innovative system that combines several technologies, maps can now include everything from traffic signs to trees.
Richard Hammersley and Gregory Orvets, Vice Presidents of Lambda Tech International, Inc., of Waukesha, WI, and Guangping He, Ph.D., have designed the GPSVision system to help cities and companies build exact maps. The combination of GPS technology, an inertial navigation system and digital imagery allows them to map such things as traffic signs, utility poles, buildings, trees, and fire hydrants.
According to Lambda representatives, GPSVision is the wave of the future where mobile mapping is concerned. "Anything you (the driver) see(s) with cameras we can locate with GPS," they claimed, adding that "it can be done quickly and accurately". Full-frame digital cameras and the GPS antenna are mounted on the van. Inside, an inertial measurement unit is used to position the van when the GPS satellite signal lock is lost due to tunnels, buildings or thick vegetation.
Easily mounted on top of or inside a vehicle, the mobile mapping system was designed to collect data at posted highway speeds. With GPS and an inertial measurement unit (IMU) accurately posititoning and directing them, color stereo digital cameras collect images at regular intervals. Signal blockages, such as tunnels, tall buildings, and trees, don't hinder accuracy, according to Lambda Tech literature.
"And not only is every picture in stereo", said representatives, "GPSVision also allows the user to know the exact position and direction of each. That, along with camera lens parameters and a baseline, make performing photogrammetry possible", he added.
In addition, data can be stored and used with any geographic information system (GIS). "GPSVision is useful to anyone building a landbase for use with a GIS.
A lot of communities [that do this] want to add infrastructure positions, which is what [our system] is all about."
By combining mobile GPS with computer processing, GPSVision is quickly able to digitally construct accurate maps. Adding digital color imagery to the picture enables the system to accurately locate and identify any [item of] infrastructure.
Applications for the process are as diverse as providing road imaging and sign locations for municipalities, location of individual trees for foresters and locations for utilities managers.
"The 'brains' behind GPSVision is a Trimble 7400 GPS receiver, which delivers a data point every second", said designer Orvets, adding that "this allows the IMU to be updated regularly".
Designer Hammersley believes the system's strongest asset is its ability to provide accurate measurement. "We can very easily measure the height of a telephone pole or tunnel clearance," he said.
HOW IT WORKS
An IMU and a GPS receiver provide accurate positioning, two high-resolution, progressive-scan digital color cameras make stereo imaging possible, digital image and data storage systems allow for digital recording, and a portable computer controls all data collection. Laser range finders and night vision cameras can be added to the system.
Processed data can be used to fix aerial or satellite imagery and to superimpose features on raster images. Vector and raster data sets can be sent to all major GIS systems, while the GPS images can be recorded or saved for future use.
Ben McCawley, road imaging project manager for Phoenix's Maricopa County, said county lawyers came to him seeking advice on how to avoid so many lawsuits involving accidents. McCawley's answer? Get before and after pictures of every traffic sign. That, he said, would eliminate 70 percent of the lawsuits because the majority of them claim that no sign existed at the time the accident occurred.
He thought this was only a pipe dream until he discovered the GPSVision system.
"With [Lambda's] product, we're going out and driving every county roadway", explained McCawley. "This", he continued, "will give the county a full inventory of signs and road striping, curbing, gutter information and road history."
"In addition, measurements of sign heights and angles will curb claims that those dimensions were at fault. In the first month of the project, which began on Nov. 1, 1996, there were 15 accidents, zero lawsuits", reported McCawley.
Because Maricopa County is the second-largest growing county in the United States, according to McCawley, it is constantly necessary to update roads and signage. Therefore, the project, which encompasses more than 6000 miles of road one way, will last five years. "With the growth we have, we probably add an extra 4000 to 5000 lane miles a year," he claimed.
The road imaging project will cost approximately $500,000 a year, all provided by Maricopa County. "That's with the understanding that we're looking at 300 accidents that we are going to be imaging and 6,700 lane miles," explained McCawley.
"This may sound like a lot of cash, but it's really not", says McCawley, "when you consider how much money the county will save in the long run. The average cost for all accidents during the past 10 years was $10 million; the average lawsuit, about $500,000. If we prevent one lawsuit, we just paid for the whole thing for one year," he said. "Not only are we reducing lawsuits, we are making our sign inventory system 100 percent accurate with still pictures of every physical traffic sign in Maricopa County."
This is important, said McCawley, because it allows the county to gauge a sign's reflectivity, thus saving the county an additional $22,000 a year because they no longer need to hire someone to check reflectivity with a flashlight.
All data will be stored in a database, with each sign given a reference number to tie it with all the signs that came before it. The sign's last replacement date, the construction of its components and its latitudinal and longitudinal measurements will also be detailed within the historical database.
"Before", said McCawley, "county employees were sent out to physically measure signs as a result of lawsuits. Sometimes juries were actually driven to the accident site to view the scene of the accident. Now, we can bring the site to them," he said. On the top of these advantages, GPSVision allows police officers to perform measurements on the computer, avoiding the usual time-consuming and less accurate tape markings.
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