The View from Above

June 1, 2000
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A new method to acquire topo data for highway design.



One of the major challenges of surveying is the acquisition of topo data for highway design. For these projects, the closure of lanes and the cost of working at night are almost prohibitive. And of course, safety is of foremost concern when the jobsite is the highway.

My firm, Mark Thomas & Company Inc., a multi-disciplined civil engineering and land surveying firm based in the San Francisco Bay area, has designed and supervised construction of over a billion dollars worth of improvements for municipal projects, transportation projects, flood control programs, subdivisions and site development.

I first saw the Cyrax Laser Scanner (Cyra Technologies, Oakland, Calif.) in July 1999. Cyrax is somewhat like a reflectorless total station in that it captures points remotely. But, it also rapidly “sweeps” its pulsing laser at 800 points per second, effectively scanning the scene in front of it and capturing it with a dense grid of points. When I first looked at Cyrax, I felt that it had potential as a tool for gathering topo information, especially the gathering of bridge and structure information. When Cyrax is mounted on a tripod, it gathers data best when looking up or down at a structure or bridge. However, I saw its inability to acquire information for roadways as a major drawback. Approximately 80 percent of our business is related to transportation, municipal and road improvement projects. Originally, I felt Cyrax would not work for our needs.

The Highway Project

In September 1999, we were given notice to proceed on the design phase of the Highway 880 widening in San Jose, Calif. This high-profile highway project included a four-mile stretch of highway widening and a bridge replacement. Highway 880 is a four-lane freeway system that carries an average of 142,000 cars daily with peak hourly volume of 10,400 cars. Because of traffic volumes and congestion, it presented several obstacles; lane closures were not an option. From past experience with this highway, I knew lane closures would be limited to four hours in the morning each day on weekends. Due to the project schedule and length of the route, weekend work would not be suitable. My thoughts turned to the Cyrax. I called Ben Kacyra, president of Cyra Technologies, and told him about the project. He set up another meeting to discuss the use of Cyrax to gather the topo data we needed.

New Capabilities for Highways

When I met with Kacyra, he had quite a surprise. Thanks to the efforts of Jack LeRoy of 3D Laservision and Doug Devine of Pacific Survey Supply, both of Medford, Ore., we had a solution to our problem. These innovative gentlemen fabricated a bracket to allow the mounting of the Cyrax scanner onto the end of a “cherry picker.” The cherry picker lifts the Cyrax scanner about 35' into the air, which allows it to “look down” at the highway surface to be scanned. I immediately saw the advantages to this approach. Highway survey data could be acquired with a high degree of accuracy and detail, and a minimal amount of danger to our survey crews. This new capability has some potentially significant implications for surveyors, as we were free to capture accurate, complete data from spatial locations at a site and from perspectives that we could never physically occupy ourselves.

We liked what we saw and had LeRoy put together a van for us to use in conjunction with the Cyrax. He delivered a van with a hydraulic boom and ground stabilizers to steady the van with the boom in place. Guy wires attached between the bottom of the boom and the van bumper locked the scanner in place and kept it from swaying at the end of the boom. The van’s interior was outfitted with a desk and power supply for the laptop computer, which partly serves as the scanner’s data collector.

The interior of the "Scan-Van," outfitted with a desk and computer.

In Field and Office

Although I counted on a learning curve for the new technology, it was steeper than I had expected. While this new device collects a great amount of data, the complexities are great as well. This equipment is not like normal survey gear. Computer literacy and survey knowledge are required to operate the device. We had a few kinks to work out with the “Van-Scan” as well.

Our first task was to come up with a plan to perform the work. Because of the nature of highway design work, we had to devise a way to scan the road, tie into our control and collect sufficient data for the design. Since Cyrax had a 40 degree by 40 degree field of view for each scan, we had to set up the scans with some overlap. The range of 50 m (at which we could ensure .02' accuracy) was also a limiting factor, although we took advantage of the system’s maximum range of 100 m for follow-on scan registration.

We decided to set three targets for each scan: two along the edge of the roadway and the third near the median. This enabled each scan to be tied to the x, y and z coordinate basis and tied to our already existing GPS network along the route. As a check, we verified each target scanned in the office using Cyra Technology’s CGP software. Each target was checked to ensure the spatial relationship between the targets matched the surveyed control.

We scanned the northbound and southbound lanes separately, although some portion of each scan covered the other lane as well. We drove the van into position on the shoulder of the roadway, stabilized it and the Cyrax boom, then did the scanning. This process was repeated every 50 m. On ramps, off ramps and bridges required additional Cyrax positions and scan targets to gather the required detail. Of particular interest were the bridge scans. We were able to scan the roadway above and the bridge structure below to create a 3-D model of the existing bridge and the road it crossed over. This allowed us to check road clearances from the existing bottom of the bridge to the roadway below. This effort also allowed us to precisely locate the existing abutments and bents to aid us in the design of a new structure.

The fieldwork for the Highway 880 project consisted of 229 scans, which took 31 days to complete (a total of 8 miles of highway topo). We did not have any lane closures; nor did we have to work at night or on weekends. Our operating window of scanning was about six hours per day. These short days were a result of waiting until morning rush hour subsided before starting and stopping before the afternoon rush hour began. The California Department of Transportation (CalTrans) wanted to minimize the gawker effect for motorists who were curious about our odd-looking Cyrax scan van.

Composite of 29 scans of the Highway 880 bridges. The text in white is the different locations of the Cyrax scanner.
In the office, all scans were checked for registration to ensure quality control. Target registration that did not fit within our tolerances was re-checked in the field. In all cases, the problem turned out to be with the survey control. This showed that the scanner was working accurately and provided a check of the original ground control.

After the insertion of all scans into CGP’s visualization software, lines were drawn along the “breaklines” for design purposes. Essentially, we did an accurate, virtual survey in the office. Instead of walking the pavement striping with a pole on the roadway, we “walked” the striping with a mouse in our office, clicking on points along the striping on the computer screen as needed. Typically, lines were drawn along the edge of the shoulder, edge of traveled way, lane marking and other key areas to help develop a 3-D surface. These features were very easy to see in the colored scans on the computer screen. Cyrax not only collects point geometry, but it also records the amount of laser energy returned from each laser pulse. Therefore, it is able to display points with different energy returns in different colors. For example, the white edge of pavement striping shows up in the scan image as a different color from the pavement. Likewise, the median railing, potholes, drainage features, etc., were easy to identify and locate in the 3-D scan images.

Scan of Highway 880 northbound looking south at the Highway 101 northbound off ramp. Signs and cars have not been removed.
Another important feature of the Cyrax system for highway topos is its ability to efficiently deal with traffic that passes through the scanner’s field-of-view. Since Cyrax can capture data on a very high-density grid (we were using a 2" grid for our coarse scans), moving vehicles that get “scanned” actually intercept a very small portion of the total number of laser pulses in each scan. These intercepted points, as well as extraneous points from shrubs, etc., are easy to remove using Cyra’s software. Once they are removed, the resulting scan cloud image looks remarkably true to the actual scene.

The lines drawn were three dimensional and exported as a 3-D DXF file into AutoCAD v. 14 (Autodesk, San Raphael, Calif). Using Softdesk v.8, a surface was created using the three-dimension linework and gridded points extracted from the scan clouds via Cyra software. After the surfaces were created, contours were then generated for the surface of the roadway. This surface also allowed us to cut cross-sections at any station along the centerline control line. This ability has let our design engineers have more information than ever before. The ability to cut a section at any location allows them to have better data to design the widening with a true representation of the highway without relying on old as-builts and previous design plans. As a by-product, quantities will also be more accurate.

To ensure accuracy, we verified the data from the scanner by taking a few shots along the road. The results of our check shots showed that the data collected by Cyrax could be relied on as much as traditional ground survey methods. Many times the data agreed within millimeters of our check shots and original ground control for the aerial mapping.

Success Leads to Another Highway Project

As I mentioned, the learning curve was steep. For example, for the first few days we were only able to collect six or seven scans a day. As we became more proficient, production jumped to 15 to 18 scans a day, or just over 1Ú2 mile each day. By the time we finished the first project, our team had the procedure down. On our next project, a survey of the south interchange of Highways 101 and 85 between San Jose and Morgan Hill, we just about doubled our production. We completed 225 scans on this project in just 14 days, with a maximum rate of 1 mile per day! As with Highway 880, we did not have to close any lanes, work at night or on weekends, or stand in the roadway to gather our data.

In terms of cost, we estimated that using Cyrax on our first project (Hwy 880) cost roughly the same as using traditional methods; however, we were able to do it much more safely and quickly, without lane closures. Plus, we provided greater detail for our road designers. On our second project, the increased productivity allowed us to achieve cost savings in addition to all the other benefits. We have other highway projects lined up for Cyrax use in Contra Costa, Alameda and San Joaquin counties. We at Mark Thomas & Co. Inc. believe that Cyrax will provide significant benefits for surveying work related to transportation facilities. The major benefits include cost savings, time savings, better data collection and safety.

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