Q&A with Chris Power of Leigh Surveyors: The New Geodetic Reality of Mobile Mapping Technology
Based in Brisbane, Queensland, Australia, Leigh Surveyors is a specialist in the transportation infrastructure market. The company maintains its leadership with continuous investment in technology, such as LiDAR and scanning/total stations, and more recently mobile scanning to deliver more comprehensive and accurate solutions, and set a foundation for digital twins. The firm was recently honored with the Best Civil Engineering Surveying Company award by Australian Enterprise Awards 2023.
We asked Chris Power, Digital Engineering Lead for the firm, to describe the trends, challenges and advantages from recent testing and deployment of mobile mapping technology.
Chris Power and Leigh Surveyors' Owner & Surveyor Rupert Leigh
Q: What’s the biggest challenge with mobile mapping for surveyors in infrastructure?
A: Accuracy. We are seeing some really impressive terrestrial LiDAR data sets around. However, a lot of these examples are relying on geometric matching or “scan-to-scan” registration to build the coverage they need without always nesting the data into a properly specified georeferenced frame. You can lose accuracy quite quickly working this way as the old geodetic problems that have been troubling surveyors for centuries come into play. We have found that by adopting tried-and-true survey workflows we can place the Trimble® MX9 data within engineering tolerances.
Q: How has more advanced scanning technology improved capabilities?
A: The ability to create precise point clouds is a genuine paradigm shift. Mobile mapping solutions, such as the MX9, open up a wide range of new possibilities. The survey equipment and software handle the geodetic issues while providing a computational environment that produces precise point clouds of any size, with individual elements only limited by capabilities such as CPU, GPU and RAM.
Q: Is there one piece of mobile scanning technology that really stands out?
A: The thing that amazes me is the IMU. Here’s an example. We were capturing a five-mile tunnel. We started with a GPS fix at one end and then drove all the way through. Without re-establishing our GPS fix at the other end, we then drove back through mapping the opposite direction. Once we ran the PPK processing, we found the IMU had drifted less than five inches over 10 miles. I wasn’t expecting that!
Q: Have you tested precision mobile mapping? What’s your workflow?
A: Over the past 12 months, we have produced almost 200 km of mobile mapped data showing motorways and complex urban environments in great detail. We are able to demonstrate absolute accuracies in the order of 20-25 mm and relative accuracies around 10-15 mm, which means these datasets can be relied on for civil engineering applications. That’s a significant breakthrough in the mobile mapping realm.
In terms of workflow, the kinds of projects we’ve been working on rely on GNSS infrastructure for Primary Control and SBET, as well as Trimble SX10 scanning total station, all brought together in the geomatic symphony that is Trimble Business Center (TBC).
In terms of 3D solids and mesh, we export reference data from TBC and create the BIM data in Civil 3D. We then import the IFC model into TBC, which can then be transferred into 12da format along with surfaces, strings and points.
Q: What are some of the near-term applications of mobile mapping now that you have those capabilities?
A: It’s that precision that opens the door for maintenance and condition surveys, pre-design surveys and as-constructed surveys. For example, the level of detail and relative accuracy attainable allows for pavement condition assessment and deformation mapping. We have also been able to model existing bridges from incidental data captured as we drive by at road speed.
The Inner-City Bypass project was one of the first large projects where we used the MX9 extensively. The specifications required a maintenance survey, but with a light touch. They didn’t want to stop traffic flow on this busy highway. We went out at five o'clock on a Sunday morning and drove the whole thing. It takes a little bit longer to register to get it down to 25mm absolute accuracy. But it's still much quicker than the boots on the ground, which on highways requires traffic control, etc., a necessary task that can be more than $10,000 a day.
We are effectively demonstrating that mobile mapping is useful for safely conducting as-built, pre-design and maintenance surveys to the highest standard without the need for road closures. The level of detail is unprecedented, and the turnaround time far exceeds the boots-on- the-ground option.
Q: What does high-accuracy mobile mapping mean for BIM and the future of digital twins?
A: For surveyors, the precise point cloud provides a step into the BIM world providing fuel for digital twins. BIM can’t avoid the reality of geomatics … and surveyors are the right people to manage it with help from today’s advanced mobile mapping solutions.
The first digital twin I created was for the M1 Upgrade highway project between Mudgeeraba and Varsity Lakes on the Gold Coast—a 6km, ~$250M Transport and Main Roads Project undertaken by Seymour Whyte Constructions. It was the first LOD500 BIM model for a highway project in Australia. Queensland Transport and Main Roads are the owner of the model, and they have used it to update their Survey Standards and Technical Specifications for construction surveying in order to integrate LiDAR technology and 3D solids and mesh into survey deliverables.
More recently, we created a digital twin for the Riverside Expressway project. The data was captured under our own initiative so that we can demonstrate our capabilities to this customer as well as future customers. We have fully documented repeatable processes, and we are just getting started.
Q: What approaches should others consider when dealing with digital twins?
A: The value of digital twins is evolutionary. The real value is realized when you see how these items present opportunities to automate important contractual processes such as quality assurance. There are strong advantages in tying together items such as takeoff, scheduling, programming, quality assurance and as-built tasks in a single evolutionary model. The platform is key!
The model starts as a design model that is aligned with a data structure to produce quantities and schedule, then transferred to a program model, which is an onsite adaptable spatial data model. This then ties design to as built by providing a practical planning platform to manage constructability assessments, design changes, set out files, and quality assurance.
By this stage, the model can be considered "as built" although it is really a quality assurance-driven change in status. QA results are added to the model, and a final mobile scanning run is then used to finalize the construction phase and capture the state of works at the start of the defects liability period.
Q: Are your customers realizing the advantage of point cloud data?
A: Absolutely. Design professionals know they can interface their designs to existing conditions with all the context and accuracy required using precise point clouds, and administrators easily adapt to the amazingly detailed reports attainable for positional conformance. Top and middle tier contractors are developing their digital engineering capability now, and the race is on to secure the best people.
Q: Any words of advice to the industry, owners/operators/contractors, who might have concerns about the use of mobile mapping?
A: In a world of increasing weather extremes, how long will it be until you can’t get surveyors to put in 10-hour days in 35-degree Celsius heat and 90 percent humidity? The industry needs mobile LiDAR systems, and the survey profession needs to offer more attractive work scenarios to attract new surveyors. If you can survey a project from the comfort of an air-conditioned vehicle, then yes, do it that way. The accuracy is there and is demonstrable.
By nature, construction is an adversarial industry, but it doesn’t have to be. Everyone knows that adversarial systems end up gridlocked. Examples are everywhere. No logical progression, just argument and deflection. We need to adopt contract structures that reward collaboration and innovation. Not just to open the way for surveying to evolve, but for the overall good of the industry.
Q: What prompted the creation of your entertaining digital twin 3D model video of Brisbane?
A: I had been making flythrough videos for a while, and I was looking for a way to shake it up a little. Something other than the usual "look at what we can do" video. The idea of a kind of superhero battle playing out in the skies over the Brisbane CBD occurred to me as a way of showcasing our model while also adding a fun side, which might appeal to the kind of technical people that work in this area. The guys at Reddish Productions took to the idea like ducks to water and produced something fun and funny while showing our model in a great context. I still get a laugh out of it, and I've seen it quite a few times by now. Check it out.
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