Case Studies: GM's Garage of Dreams Captured in 3-D
GM brands are as widely known as their automobiles, and their brand equity has generated a highly lucrative sideline business through the licensing of GM trademarks. The trademark team looked for existing technologies producing highly accurate full-body vehicle scans-interior and exterior-to create usable models that could be supplied to trademark licensees.
A world-class garage of automotive dreams is tucked away in an unassuming brick building in a Michigan industrial park. Inside lies the legacy of General Motors in all its shining chrome glory. More than 100 years of automotive history and one of the most influential collections of automotive design is housed in the GM Heritage Center, an 81,000-square-foot facility located in Sterling Heights, MI. The center is not open to the public and mainly used for internal GM functions, although it is available for rental for special events.
Inside the showroom, you will see aisle after aisle of rare vintage vehicles from first-off-the line production models to one-of-kind concepts. This is no dusty archive! Virtually every one of the more than 200 vehicles is fully operational, and travel constantly to auto shows and other special events. Cars are driven through wide showroom aisles to several transport semis on standby for the next event.
Even those with a mild interest in automobiles will marvel at the wealth of instantly recognizable vehicles-the ’57 Chevy Bel Air, the Pontiac GTO, a family of Corvettes of every vintage and some designs never intended to be made but hold their place in automotive history. A good example is the late 1950s series of Firebird jet-turbine powered concept cars for GM’s “Motorama” exhibit. We’re still not driving cars guided by wires embedded in the highway, but GM envisioned and prototyped the idea by way of the 1956 Firebird II.
GM's Heritage as Brand Equity
GM brands are as widely known as their automobiles, and their brand equity has generated a highly lucrative sideline business through the licensing of GM trademarks. Envision the Chevy “bowtie” or the Cadillac “crest" on all sorts of items from shirts to keychains. GM car body designs are also trademarks. Every diecast collector vehicle or Happy Meal toy that mimics a GM body is a licensed product. GM’s licensing program is the world’s largest, generating more $3.4 billion in end retail sales from licensed products, according to Equity Management Inc., who manages the GM trademark program.
What does GM’s trademark licensing program and the GM Heritage Collection have in common? Charlie Robertson, VP of Equity Management, explains, “The accuracy of the licensing program is very important to GM for the protection of their brands and the integrity of the trademarks. We have a team of people that review every single licensed product that is put out into the marketplace for accuracy and appropriateness. In the past, if the licensee was making products that reproduced body styles such as diecast or plastic models, even things like clock radios and specialty chocolate-we left the task of ensuring an accurate reproduction of the body in the hands of the licensee, and they had to sort of figure it out on their own. If what they came up with wasn’t right, we would ask them to make changes, of course, but we knew there had to be a better way.”
Scanning the Stuff of Dreams
The better way turned out to be precision 3-D scanning of important examples in the GM Heritage Collection. The trademark team turned to Steve Ellison, engineering manager at GM’s Manufacturing Engineering Technology group in Warren, MI. This group evaluates new 3-D scanning technologies for assembly and quality assurance, and then determines how best to apply them to GM’s manufacturing operations around the world. The trademark team asked if there were any existing technologies producing highly accurate full-body vehicle scans-interior and exterior-to create usable models that could be supplied to trademark licensees.
Fortunately, Ellison’s team had several ideas based on their usage of 3-D scanning technologies at various GM manufacturing facilities. These included the CogniTens Optigo “white light” scanning system and the Romer Infinite 2.0 portable arm coordinate measuring machine (CMM) with a ScanShark laser scanner. Both are products of the Hexagon Metrology (North Kingstown, RI) group of companies. Chris Purdy and K.C. Hahn, technical experts from the Manufacturing Engineering group, were sent to the Heritage Center to launch the new scanning project.
“Providing an accurate computerized 3-D model as part of the trademark licensing process is an important value-add for the GM program, making it a more attractive opportunity for the licensee,” noted Charles Robertson. “Having 3-D models available of the licensed body style provides a double benefit. First, it ensures that the reproduction is as accurate as possible for the protection of GM’s brand. Secondly, it makes the process of transferring the design to a licensed product so much easier on the part of the licensee. It also allows a far greater amount of detail than ever before. One of our fastest growing licensing avenues is video games. For them, having a 3-D model to work with makes their work that much easier, and the result that much more realistic.”
To start, the team is focusing on a relatively small slate of about a dozen vehicles--some that are rarely reproduced and other representing milestones in GM design history. Among those planned for this first round of scanning are GM concept cars: the 1959 Cadillac Cyclone, 1985 Corvette Indy, the 1987 Oldsmobile Aerotech, and the 1959 Corvette Stingray Racer, plus the production 1957 Cadillac Eldorado Brougham.
Chrome to Cloud: Capturing a Classic Caddy
Purdy and Hahn began the project with the 1957 Cadillac Eldorado Brougham, an extraordinary example of the most exclusive and technically advanced production vehicle of its day. The team first completed a fast scan of the major surfaces of the car’s body using the white light scanner, the Cognitens Optigo. This device projects a specific light pattern on a surface, then optically captures the contours of the surface beneath the pattern in a millisecond-long flash with three cameras mounted in the “head” of the device. The scanner sits on a rolling stand and is moved around the vehi-cle methodically-project-flash-capture-move, repeat. A highly accurate, though incomplete, model of the vehicle is captured in less than 1 hour. The resulting data file is a point cloud, a mathematical model of the 3-D position of all surface points gathered in relationship to one another.
Point clouds can easily top hundreds of millions of individual data points when scanning something as large as a car. A series of retroreflectors, that look like white dots, are placed on the surface of the vehicle that allow the scanner to “see” the reference surface of the car, as shown in the photograph. The dull appearance in the photo is nothing more than a light haze of car wax. “Dulling down a shiny finish gives us more accurate results with the Optigo,” said Hahn. The objective of the fast scan was to evaluate the technique of first capturing the major structure of the vehicle, then filling in the details with the portable arm-mounted laser scanner as a second step. “We didn’t wax or put reflectors on the roof, as we didn’t want to risk damaging the stainless steel. Fortunately, the ScanShark laser on the Romer arm has no problem with these surfaces, so the wax and the reflectors would have been unnecessary.”
The white light scanner delivers a get-in-get-out-quick approach to the task, while the articulating arm delivers a more nuanced approach. The portable arm measuring machine functions in many ways like a human arm, it has a “shoulder,” “elbow” and “wrist”. The arm can rotate infinitely in four of its joints, which is handy for getting into tight spaces. Mounted at the business end of the arm is a triangulation laser scanner, called the ScanShark V5. The scanner has a pistol grip handle that the operator holds to project a line of laser light on a surface. An integrated camera reads the reflection of the light off the contour of the surface. This all happens with incredible speed and precision.
The scanner projects over 7,600 points per laser line and 60 lines per second-translating into a data collection rate of more than 458,000 points per second, with point to point spacing of less than 0.0005 inch. However, since the arm/scanner combo is handheld, it allows the user to carefully and deliberately pass over the surface to be scanned. This is sometimes referred to as “painting” the part-as the points appear on-screen in the software, spray-paint like, as the scanner operates. Hahn explains the approach for the fill-in scanning. “Transferring the point cloud we gathered using the Optigo into Polyworks software (Innovmetric Software Inc., Quebec City, CA) allows us to add the additional laser scanned data to the point cloud in real time, while remaining in the same reference frame. This is important to make sure the new scans and the old data are aligned perfectly. So we are essentially adding the Romer data on top of the Optigo data to fill in the missing pieces. Normally in production, we use the Optigo on something like a single piece of sheet metal-a door or a hood-which works quickly and very well. But a complete vehicle is more complicated.” Purdy agrees, "This Cadillac has a lot of edge data, and other areas that are difficult to entirely capture with the Optigo…areas like the cut lines, side spears, the filleting in the hubcaps and the inside of the wheel wells.”
Using the original point cloud that was imported into the software as their guide, the team zooms in on specific areas of interest and begins to fill in the details with the Romer Infinite 2.0 arm and the ScanShark scanner. These fine details include the cut lines where the body panels meet, hidden areas, areas with depth, the area under the door sills, the grille and headlight brows and all sides of the rear view mirror.
“The cut lines in particular [where the body panels meet] are particularly important to get accurate for making scale models, and the laser is great at capturing the entire roll of the edge,” comments Purdy as he passes the scanner over the car at a deliberate, measured pace. On the computer screen, the point cloud steadily transforms into the vehicle in front of them. With the 458,000 point per second data rate, the ScanShark gathers so many points so quickly that recognizable swaths of the vehicle appear with each pass, including scanning that stainless-steel roof. Because of the scan path of the ScanShark’s laser is more than 4 inches wide, Purdy is able to capture the entire roof panel in just a few minutes.
The complete interior of the vehicle is scanned with the 12-foot articulating arm reaching deep inside the interior to scan the seats, the chrome dash, the chrome speaker grilles in the back seat and all the other surfaces. The ScanShark probe can scan all different types of surfaces with no surface preparation, which is particularly convenient with all the chrome parts. The final step is scanning the entire engine compartment, including the vehicle ID badge, which clearly identifies this specimen as #359.
StingRay meets ScanShark
A guttural growl echoes through the shop as the next vehicle is driven in. As the Cadillac was all about elegance, the next dream machine exudes nothing but testosterone and adrenaline-it is a one-of-a-kind 1959 Corvette Stingray Racer.
The Stingray is placed on a portable lift to raise it several feet up for the team to scan its nearly featureless underside. It is then lowered to the floor for a full-body scan, including inside the engine compartment, which is accessed by raising the entire hinged front end, fenders and all-a feature not found on production Corvettes until the 1980s. The spare tire compartment hinges backward in a similar manner.
Purdy and Hahn scan this vehicle entirely with the laser scanner and arm as it is low to the ground, has no roof, and it is easy to reach by barely moving the arm from its original position. The sparse cockpit features little more than the wheel, five gages, the gearshift and a fire extinguisher, as well as the original silver leather seats. The entire vehicle, despite its in-your-face appearance, has rather diminutive proportions. The 92-inch wheelbase is more than a 14 inches shorter than a production Corvette of today, and the two-part windshield is so small it barely comes up to the driver’s chin.
We Have Point Clouds, Now What?
The vehicle scan files are broken up into several separate 3-D files to ease manipulation and cleanup of the scan data, and to keep the file sizes smaller. Sections are overlapped by several inches to aid the eventual merge of the scanned sections into one complete model. Or, as it turns out, half a model. Since the exterior of vehicles are generally symmetrical, just over half of the exterior is scanned-to just a few inches across the centerline. The entire model will be mirror-imaged later to make a complete car, with the exceptions including the hood ornament and the windshield wipers. Several reference sections were scanned on the opposite side of the Eldorado to ensure an accurate side-to-side match with the mirrored file. The StingRay's rear half is non-symmetrical so the entire area needed to be scanned.
Post-processing of the data files occurs back in GM's Warren offices. The process starts with cleanup of the point clouds to eliminate unnecessary details such as the floor or stray points caused by reflections. The point clouds are converted by Hahn and Purdy into polygon mesh models, a series of interlocking triangles, followed by merging of the individual files, and the eventual mirroring into one 3-D model representing the entire exterior of the car. Internal components such as the engine compartments and the interiors are modeled separately at the same reference size as the exterior model.
The eventual output for many uses is an STL file, which is a generic 3-D file type most associated with rapid-prototyping 3-D printers used to create physical 3-D models. For highly detailed applications, the mesh data will be transferred to Aaron Lemmert, a CAD surfacing expert in GM Design. Lemmert will reverse engineer the meshes into NURBS surfaces, much like an original CAD model. The time invested per vehicle? Approximately a day to collect the raw data each exterior, two to three days of file cleanup, and four to five days of post-processing to achieve the final file, depending on the complexity of the vehicle. According to Hahn, a good general estimate for any 3-D scanning project is that it takes roughly two to three hours of post-scan work for every one hour of scanning.
The objective for GM's trademark licensing group is to eventually provide complete 3-D files for licensees for as many classic GM vehicles as possible, which Robertson views as a huge selling point. At this point, Robertson's telephone rings and he excuses himself to talk with Sony about a licensing deal for a new video game. Looks like GM’s garage of dreams meets the stuff of virtual dreams.