Using Cyrax scanning technology, David Evans and Associates Inc. (DEA), Denver, surveyed 24 bridges in 40 days without disrupting traffic on the heavily traveled I-25 through the Denver metropolitan area. T-REX, the Transportation Expansion Project launched by the Colorado Department of Transportation (CDOT), includes highway expansions, improvements and the addition of light rail along 18 miles of I-25 and I-225. The $1.67 billion design-build project includes reconstruction of interchanges and bridges, a new drainage system and improved pedestrian and bicycle access. One of the goals of the project is to accommodate the addition of a light rail along sections of the interstate.
CDOT selected Southeast Corridor Constructors (SECC), Denver, for the project, based in part on SECC’s aggressive work plan for finishing T-REX 22 months ahead of CDOT’s schedule. SECC is a joint venture be-tween Kiewit Construction Co. and Parsons Transportation Group (PTG). Turner Colley Braden (TCB), Sverdrup and DMJM are assisting PTG in the project design. Kiewit is responsible for gathering the necessary design survey information as well as construction staking and final right-of-way surveys. DEA was hired as the design contractor of the project.
Time was a critical element, as was the need to avoid lane closures during surveying. A total of 22 structures (out of a total of 67) needed to be surveyed with a combination of Cyrax and other terrestrial survey methods in 40 days.
Traffic, crew create a buzz
After reviewing the tight schedule and design requirements, Jim Bodi, survey manager for SECC, decided to combine conventional terrestrial surveys with aerial mapping and to use a Cyrax scanner to gather the bridge and mainline freeway as-built data. He hired my company, DEA, to provide terrestrial surveys and Cyrax scanning services.
My task as the survey manager was not made easier by the fact that DEA crews had 40 days to complete field surveys for base maps of 24 bridge sites over or under I-25. Right at the start I decided we needed two Cyrax crews for the Cyrax scanning and three field crews. DEA performed mapping under and over many structures while six to eight lanes of traffic buzzed by uninterrupted. In the office, DEA employed six survey technicians to manage the Cyrax data: three to process the data, one to process the field survey data and two drafters to produce the base maps.
We learned a lot. One of the more amazing facts related to this project is that even with five field crews working 12- to 16-hour days we did not require traffic control or lane closures for any of our work. We worked through morning and evening rush hour while listening to the helicopter traffic reports on the radio talk about the work we were doing, but at no time did we impede the flow of traffic.
The Cyrax scanner has been used for the past three years; however, it has never been put to work on so many structures in such a short time. DEA had extensive experience using the Cyrax equipment and processing the data for bridges, intersections, roadways, parking lots and buildings. Our survey technicians are trained and experienced in merging the scan data with the field crew’s topographical mapping to prepare maps for design.
For those who are not familiar with the 3-D laser scanning, the Cyrax system is a self-contained unit that consists of a scanner the size and weight of a small computer monitor, a power supply, a Dell laptop computer and the Cyclone software installed on the laptop. The scanner sweeps a green eye-safe laser over the area it surveys and with each sweep gathers 1,000 points per second. It has a practical range of 180-200 meters (594-660 ft), and it is calibrated to achieve survey grade (6 mm/0.24 in.) precision of each individual point for up to 50 meters (165 ft).
In a few minutes the scanner captures up to 1 million points and displays these as a dense “point cloud” on the laptop’s screen. Looking at the point clouds is almost like looking at a photo, except that this “photo” is 3-D and can be rotated and viewed from every angle. In addition, Cyclone allows for the registration (stitching together) of many individual scans, which could come in handy when surveying a large bridge or building or when scans are taken from different angles to capture all sides of an object. Further, Cyclone provides a powerful set of tools to semiautomatically convert point clouds into 3-D CAD objects, which in turn can be exported to AutoCAD or Microstation. This last feature was important to us, as our deliverable to the clients was 2-D CAD drawings either in AutoCAD or in Microstation.
The bottom line is that we knew it would work for T-REX and believed we had the right combination of field and office procedures to complete this project in the time allotted. The further we got into the work, the more we found our normal survey procedures also applied to the new technology. Even though the scanner collects data differently (quicker and more of it), the same type of control is necessary. Each scan has to have at least four control points or registration points in it. If the control is poor, the scan data are useless. Proper planning and attention to detail is essential for a successful project.
The way it was handled
We used one scanner mounted on a tripod and the other scanner mounted on a boom truck, dubbed the Scan Van. The tripod scanner performed the under-bridge scanning and tight-area work, while the Scan Van provided proximity for the railroad scanning and mainline work. The Scan Van has a boom arm that raises the scanner and increases the range and visibility, thus increasing the amount of data that is captured. We could park off the shoulder with the van and scan the freeway while the cars drove by. The cars would show up in the scan as a single line. The scanning technicians could then delete the cars from the scan before sending the data to the mapping technicians. If the traffic was going very slowly or was stopped we did not attempt to scan.
We also learned that by setting up a conventional instrument, such as total stations with each scanner, we were able to increase our productivity. We could tie in the control points while the scanner was operating and pick up the obscure area topo the scanner could not observe. The scanner can only pick up what it can see, therefore the top of a curb may be mapped but the flow line would not be measured. Likewise, we found that areas around parked cars, guardrails or brush could be mapped using the conventional instruments.
This is so far our largest deployment of Cyrax technology that we used in conjunction with other methods. In fact, the main challenge was to coordinate the use of a number of different hardware and software platforms. These included the Cyrax systems (used mainly on bridges and overpasses) and total stations, aerial survey and GPS equipment for the main roadway and control. The Scan Van-mounted Cyrax achieved about 240 ft distance and the tripod-mounted Cyrax about 180 ft.
DEA used the following work flow:
• Collect control survey data and Cyrax scan data—two-person field crew;
• Process survey data in Listcad (create control point coordinates);
• Load survey control data into Cyclone and register scan data (in-cludes quality control check of registration);
• Prepare 3-D polylines of all key break lines and bridge features. Line types are assigned colors and are put on appropriate layers for later use in AutoCAD;
• Launch AutoCAD from Cyclone and save file as AutoCAD;
• Review line work in AutoCAD and correct any layer errors; and
• Translate from AutoCAD to Microstation (InRoads) for final file/ drawing preparation.
Final deliverables to the client were Microstation files for 2-D planimetric drawing files and divisional terrain models (DTM) for contours. The client can use planimetric drawings for their horizontal designs and the DTM for all of their vertical calculations. DEA delivered the survey on time and on budget.
All in all we spent 40 days scanning in the field using both Cyrax 2500 (Circle 935) scanners with a crew of two for each. During this period we took about 400 scans. In the office it took the office crew 50 days to model all data, but since they worked parallel to the field crews they were able to finish modeling 10 days after the last scan day.