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We see street curbs and gutters every day but never give them a thought (except when we trip over one and land in the other). So most people have no idea how they’re made, much less how Reality Capture is improving how they’re made.

As evidenced by articles in this blog, Reality Capture is being used for very exciting and newsworthy endeavors…from virtual reality and the digital resurrection of the Buddhas of Bamiyan, to saving Hawaiian coral reefs and mapping Finland’s forests. Curbs and gutters aren’t quite as glamorous.

But picture this. Imagine concrete curbs and gutters that are automatically extruded by a giant souped-up Play-doh Fun Factory on wheels being guided by laser beams bounced off satellites in orbit around the Earth! More interesting, right?

Increasingly, that’s exactly how curbs and gutters are being built. For highway, road, and even parking lot construction, many contractors are starting to replace conventional survey and control methods with stringless grading and paving equipment controlled directly by Reality Computing technologies in the form of model-based design, GPS-guided machinery, and laser control systems.

Stringless Curbs and Gutters, cropped

Credit: Summers-Taylor

Traditionally, curbs and gutters (as well as median strips and even sidewalks) are built using a slipform machine—aka the giant souped-up Play-do Fun Factory on wheels. Survey crews locate and place stakes representing the location of the curb, and then place a stringline from stake to stake. This stringline creates a reference line for the slipform curb machine, which has wands that sense position and control elevation and steering.

Whereas GPS-guided stringless machines eliminate the need to set stringlines on jobsites, which cuts back on both time and labor costs. These machines rely on Reality Capture in the form of laser scanners, 3D digital design models, and GPS technology to capture, compute, and create curbs.

Capture: To support automated construction, civil engineers use 3D design software such as Autodesk Civil 3D to design, analyze, and visualize the civil engineering project. The starting point of the design process often involves laser scanning or other survey techniques to digitally capture existing terrain conditions in the form of a point cloud.

Compute: This point cloud is uploaded to the 3D design software to guide/inform the civil engineer’s design. The final civil design model details the new construction (such as the road or parking lot) as well as graded topography that meets the surrounding terrain. When the project is ready for construction, model-based design information, including concrete curb and gutter layouts and elevations, are transferred to GPS-guided machinery.

Create: Rather than using stringlines and wands to control steering and elevation, GPS-guided curbing machines automatically read the digital curb design and extrude concrete curbs at the proper elevations.

The fine print

But as if often the case, the “devil is in the detail”. And when it comes to GPS-guided machinery, the aforementioned detail is literal. GPS navigation systems on a ship or a plane, or the ones in your car or on your phone, are accurate to within 10 or 20 yards. When you’re following directions to the nearest coffee shop, this accuracy is fine—but not so much for construction.

So GPS-guided construction machines use an auxiliary positioning system: a GPS base station. This is a separate GPS receiver mounted over a point with known coordinates and located near the construction site. It receives the same satellite errors as any other GPS receiver. But because it knows its true position, it can calculate and communicate the corrections to the GPS-guided machinery, increasing the accuracy to within an inch or so. For even more accuracy, readings from laser-based total stations can be combined with GPS horizontal positions to calculate extremely accurate elevations.

By combining GPS and Reality Capture technologies, construction firms can go straight from a 3D design model to the installation of curbs and gutters.

Curb appeal

Reality Capture and GPS-guided construction equipment is a boon to contractors and their clients. For example, a Tennessee-based heavy construction contractor reports that they are 20 to 25 percent more productive  with stringless curb machines. A construction firm in Ontario reports that they have experienced a 10 percent savings  in concrete use.

And Reality Capture technologies to capture, compute, and create stringless curbs are at the core of these savings.

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