- SPECIAL REPORTS
- THE MAGAZINE
When the Community Redevelopment Agency of the City of Los Angeles (CRA/LA) set out in early 2009 to develop a new pedestrian-friendly and efficient transit corridor that would link the city’s southern region with downtown, the management team had a clear vision for what it hoped to accomplish. A public agency promoting community growth and prosperity, CRA/LA has worked with numerous private investors to revitalize neglected communities in the region. The challenge for the management team, as always, was conveying its vision to investors and the communities that would be affected by the development work. Wouldn’t it be nice if the original surveys could somehow capture enough details about the corridor to make it easy for all of the stakeholders to visualize the possibilities?
They could−and Donald Spivack knew how. As deputy administrator of CRA/LA, Spivack had overseen dozens of surveys on past projects, most of which were handled through traditional means using total stations and data collectors. Then, in late 2008, Spivack saw a demonstration of mobile scanning technology. The results were impressive. “All of the data were presented in a visual format,” he says. “It was a tool that could really help us convey our project vision to everyone involved.”
The CRA/LA management team decided that the surveys for the new transit corridor would be obtained entirely through mobile scanning, and it sent requests for proposals to all of its on-call service providers. Several weeks later, Diamond West Inc., a multidisciplinary planning, engineering and surveying services firm located in Calabasas, Calif., was awarded the contract. “We have a static scanner and have been doing streetscape work and other scanning projects for more than five years now, so we felt very comfortable with the requirements of this project,” says Mike Harrison, president of Diamond West. “However, this was our first mobile scanning project. We wanted to make sure we got it right.”
An Ideal Partnership
This flythrough was generated from RGB color point clouds based on data obtained by Terrametrix with the StreetMapper mobile LiDAR system.
Harrison knew that ensuring a successful outcome would require working with the right partner. He had heard about Omaha, Neb.-based Terrametrix LLC and its StreetMapper mobile mapping system (developed jointly by IGI mbH and 3D Laser Mapping using Riegl scanning technologies) through conferences and colleagues, and the firm seemed like a good fit for the CRA/LA project. As he was drafting the proposal, Harrison contacted Michael Frecks, PLS, president and CEO of Terrametrix. “We really hit it off,” Harrison says. “Mike had the same kind of vision about scanning--what it is, how it works.” After just a few conversations, Harrison was confident enough to include Terrametrix in the proposal.
The two firms immediately began coordinating the details of the target placement and scan work. The project would involve scanning 22.7 miles of streetscape--including building facades, two- and four-lane urban highways, adjacent light rail lines, and 300 feet in both directions at approximately 183 intersections. Diamond West would set the primary and secondary control using GPS and robotic total stations, and these data would need to be meshed with the mobile LiDAR data captured by Terrametrix. To streamline the project, the firms agreed to use targets posted on utility structures, walls and utility boxes in a vertical plane for secondary control rather than the more time-consuming process of painting horizontal targets.
The scans would be captured at 10 to 15 mph in a busy urban canyon environment, so planning of the driving route was crucial to minimize traffic and other “noise” while ensuring a good dilution of precision for GPS positioning. Colorized point clouds were needed, so scanning at night wasn’t an option. The teams would have a limited window of opportunity to complete the scans during off-peak daylight hours. “Mobile mapping is fast and has the ability to reinitialize through closely coupled IMUs [inertial measurement units],” Frecks says. “It was the ideal solution for this project.”
The Diamond West crew arrived onsite in late March and began setting the control for the surveys using both static and RTK GPS along with robotic total stations. The primary control was based on California Coordinate System of 1983 Zone V (CCS83, based on NAD 83) and the current City of Los Angeles bench mark network. All secondary control points were referenced to the primary control. Within two weeks, all 400 control points were in place, and the stage was set for Terrametrix to begin the scan work.
The four Riegl LMS-Q120 scanners used in the original StreetMapper system were capable of performing accurate high-resolution scans in complex environments. But for the CRA/LA project, Terrametrix wanted to capture the maximum amount of data on the building façades in the cleanest possible format. Adding Riegl’s new VZ-400 to the StreetMapper system allowed the firm to achieve these goals while also increasing the system’s data capture speeds from 40,000 points per second to 165,000 points per second.
Despite challenges such as parked cars obscuring the scanners’ field of view, high-rise buildings limiting GPS coverage, trash collection, road closures for movie filming and event traffic for LA Lakers playoff games, Terrametrix completed the scan work in four days. More than 2 billion points of data were collected in all. “The VZ-400 wasn’t available during the first two days of data acquisition, so we actually scanned the project twice during our four days onsite,” Frecks says. “The additional days of data collection with the VZ-400 increased data coverage in areas with parked cars and traffic movement because we were making an additional pass of the entire project at a different time of day.”
Scanning the corridor turned out to be the easy part; working with the data proved slightly more complex. Terrametrix processed the scan data with Terrasolid software, running under MicroStation V8, dividing the point clouds from the entire 22.7-mile scan into 176 blocks of 600 feet. Each block file contained 10 million to 15 million points. To colorize the point cloud from the onboard video system, Terrametrix added place holders for the RGB values. The raw point cloud data were delivered to Diamond West in ASCII files within a few days of completing the scans, as planned.
From there, it took Diamond West 12 weeks to develop the CAD deliverables for CRA/LA. “We had to do some manipulations and conversions of the data to get it into a format we could work with to generate the topographic maps, which was a bit of a challenge,” Harrison says. “There was also a lot of cleanup work involved.”
By developing a linear equation to scale the point intensity values, Diamond West was able to successfully import the data into its Leica Cyclone II TOPO software. From there, the firm performed extensive cleanup of pedestrian and automobile traffic, extracted the required planimetrics and created 3D line work. Those files were then imported into Autodesk’s AutoCAD Land Development Desktop, which the firm used to create detailed digital terrain models. “Usually when you think of surveying, it’s like a 1-to-2 comparison--one day in the office for every two days in the field,” Harrison says. “But that kind of comparison doesn’t apply with mobile scanning. It [working with the data] is a very tedious process. As the tools continue to develop, that part of the process will go faster.”
In fact, it continues to work out well. With more than 2 billion highly accurate points at its disposal, Diamond West expects to mine additional value from the data as the firm works closely with consultants on the next phase of the CRA/LA corridor project and pursues other projects in the region.
“At the end of the day, it’s about managing billions of points and doing so efficiently,” Harrison says. “I think scanning in general--whether mobile or static--is the future of surveying.”