NASCAR scanning article for Trimble Navigation

This article was written for Trimble Navigation, the world’s largest maker of GPS and survey equipment. It is just one of dozens of case studies I’ve written (under the pseudonym Craig Dylan) for Trimble that establish them as the preferred equipment choice of land surveyors and engineers. The articles typically appear in surveying trade journals, but also in magazines devoted to factory management and the energy industry.

Updating the Lady in Black – 3D scanning infuses new life into NASCAR’s first superspeedway.

NASCAR racing is rich in tradition, and no NASCAR track is home to more legends than Darlington Raceway in South Carolina. Known as the track that’s “too tough to tame”, Harold Brasington began construction in 1949, making Darlington the first superspeedway built specifically for NASCAR racing.

NASCAR-scanning-articleBrasington, a retired racer, knew that wide, sweeping turns were a necessity for the high speeds of a NASCAR event. But the 70 acres of cotton and peanut fields he bought had one limitation: the seller, Sherman Ramsey, insisted that his minnow pond remain undisturbed. So Darlington Raceway ended up egg-shaped, with a long and broad turn at the east end of the track, and a considerably tighter, narrower and steeper turn at the west. This unusual configuration turned out to be Darlington’s most important feature; drivers say it’s hard to get in a groove, that the track rewards skill, and that more than a fast car is needed—that’s why Dale Earnhardt said, “if you happen to be a race car driver there’s no victory so sweet, so memorable, as whipping Darlington Raceway.” Consequently, a good performance at Darlington is a badge of honor, and when rookie drivers hit the wall there, as they often do, they’re said to have earned their “Darlington stripes.”

But aside from the track, not everything about Darlington Raceway is ideal from a fan’s point of view. Unlike many NASCAR facilities, Darlington is not located near a big city or other attraction, so a trip to the races doesn’t fit well with a family vacation. Attendance has been falling off in recent years, and some have wandered if the “Lady in Black” (so called because of the tire marks that darken the track’s barrier walls) will be able to survive in the modern era. To woo fans, there have been major investments in recent years, including the addition of lights in 2004 to support nighttime racing. The biggest investment to date began in early 2007, when the current owners decided to put $10 million into repaving, the first complete repaving since 1995.

Preserving character

Repaving was definitely needed. NASCAR tracks see a lot of abuse, and Darlington’s  steeply banked turns—23º and 25º—were shedding asphalt; there was rutting, exposed aggregate, failing subgrade and in some places pavement was actually slipping down the track. Also, a lot has been learned about optimum track shape since Darlington was built, and some tweaking was needed for speed and safety.

But at the same time, Darlington’s most bankable asset is it’s ‘racer’s racetrack’ character, and if the track turned into just another modern superspeedway a lot of priceless tradition would be gone forever. An extremely accurate survey of the track was needed, to ensure a faithful reconstruction, and an accurate 3D model would be needed for use in the specialized software used to analyze track characteristics. Raceway officials mandated survey shots at 3-inch spacing, with accuracies of at least a hundredth of a foot vertically and three hundredths of a foot horizontally. Since the track is a lot like a 1.4-mile section of highway, complete with barrier walls and other features, this would amount to millions of shots, and lead contractors Sunmount Construction decided that 3D laser scanning was the best available technology.

This would be the second time scanning was tried at a NASCAR track. The first attempt, at Talladega Superspeedway, was not a complete success, due to accuracy issues. So Sanborn Map Company, Inc., the subcontractor hired to do the scanning, knew they had their work cut out for them. “We did our due diligence on this one,” says James P. Peterson II, PE, PLS, Sanborn’s Vice-President.

A challenging job

Sanborn used a Trimble GX scanner for this project, and after consultation with Trimble, decided to set a maximum scanning distance of 500 feet for this project. The GX will scan much further, up to 1,100 feet, but the low angle of incidence of most track shots, and the relatively tight accuracy requirements, suggested a lower limit. This meant that a large number of control points would need to be set, and that a larger number of discrete scans would need to be registered.

Weather turned out to be a surprisingly important factor. Scanning was done in June, and the acres of pavement pushed daytime temperatures well above 80º. Temperatures inside the scanner were even higher. Peterson found that the GX handled temperature differentials quite well, that is, data was as accurate at 40º as at 99º, but at internal temperatures over 104º data was unreliable. An umbrella was used effectively, but when sun angles were low, he occasionally had to shut down for an hour. Peterson says that the galvanometer and other atmospheric correction features on the GX were so essential that without them he, “couldn’t have done the job—there would have been 0.3’ busts everywhere.” Still, though gathered data did stay within tolerances, there was observable degradation on the worst weather days.

Barrier walls were also ‘barriers’ to scanning, mainly because the obstructed sight lines would create ‘shadows’ that could have doubled the number of scan setups. To get around this, setups straddled the wall, or alternated from one side to another, and were on tall tripods with the scanner up to ten feet high. Ladders were used to set up and level the GX, and were also needed to determine the height of the setup—the ladder work turned out to be one of the project’s more tedious aspects. High setups also led to large unscanned areas directly beneath the scanner. Typically, these were ‘backscanned’ from adjacent setups, but in a few cases a total station was used to fill in scan shadows.

Deliverables for the project called for stripes to be located accurately. Since scanning would not normally pick out painted stripes, this could have meant a lot of extra total station shots. But the GX, controlled by Trimble PointScape software, took georeferenced photos that could be aligned with known points in the scanned data. Peterson says, “One of the cool things about the GX was that we were able to take images from the scanner and apply them (in Trimble RealWorks) to the mesh created from the point cloud. We were actually able to survey the paint striping from the image, and didn’t have to take separate shots except as a check.”

Edge detection, especially important in corridor surveys like this one, is traditionally a problem with scanning as the scanner doesn’t necessarily take shots exactly at toes and other breaklines. Some conventional shots were taken for quality control, but Peterson relied mainly on Trimble RealWorks’ edge detection tools, and found they worked well.

Tight control

Sanborn used rapid static GPS to set 21 primary control points around the track. South Carolina State Plane Coordinates were applied; this was done because aerial photography was part the project, and georeferencing would help tie the scanned data to orthophotos. A Trimble 5600 Robotic Total Station was used to densify the control network and create ample options for backsights and setup points—plenty of control meant there would be little temptation to stretch scan limits beyond the 500 foot maximum, and a primary control point could be observed from every setup.

Survey Workflow, a feature introduced on the Trimble GX, proved invaluable for this large scanning project. Essentially, Survey Workflow means that the GX can be used to traverse around a site much like a conventional total station. The GX can be leveled, and backsights and foresights taken as part of the setup process. Peterson says, “The ability to zero index the galvanometer, thermo indexing, atmospheric corrections, realtime level compensation, and a dual axis compensator has allowed for a more traditional survey workflow. The user can calculate the position of the scanner by normal traversing or resection. It creates flexibility, and I wouldn’t want to do a job like this without this ability. Without Survey Workflow, each scan setup would have started at zero zero, and in the office, all the scans would have been stacked on top of each other. This way, we were able to check scan data as it was gathered, and could use PointScape to check setups and registration, and avoid drift. It made a big difference.”

For each scan, the GX was set up on a known point, and four more known points were shot: “three points for the plane, one for a break in plane, and one to throw out,” Peterson explains.

This was a sensitive job, and accuracy and reliability were of more than ordinary importance. So Sanborn took the unusual step of hiring a second survey firm to traverse the primary control network and to shoot eleven track profiles from barrier wall to barrier wall. After scanning data was registered and processed, these profiles were used to verify that scanning data was within tolerance. Overall, after checking, Peterson was very pleased with the accuracy of scanning data and found that residual error was within tolerance for the entire project, making the scan of Darlington Raceway the first totally successful application of scanning technology to a NASCAR track.

Getting it right in the office

PointScape and the GX’s Survey Workflow meant that scans came to the office with a ‘phase one’ registration, meaning that data was where it should be, but might benefit from reevaluation. Field operators were instructed not to worry too much about which configuration of the four backsights yielded the most accurate resection. Office staff went through various iterations of control data, and made a few adjustments to fine tune results. Occasionally, holding fewer backsights gave better data.

After an acceptable point cloud was created, profiles from the quality control surveys were imported. These profiles were checked against the scanned surface visually, to catch large errors, and then a digital terrain model (DTM) was created so that the vertical coordinates of the quality control profile shots could be compared to points at the same horizontal coordinates on the DTM. Results indicated that the scan was acceptable. RealWorks was then used extensively to apply breaklines and further refine the track model.

Although it would be possible to perform a scan where control coordinates are not known, and rely on office technique for registration, Peterson believes that this would be a mistake. The advantages of field registration and checking against known coordinates are just to great.

Tools of the future preserve the past

There is no escaping the futuristic appeal of scanning technology. The largely automated, extremely rapid collection of huge amounts of data, and the easy conversion of that data to accurate 3D models, complete with photographically accurate appearance, would have seemed like magic just a decade ago, and still has the capacity to astonish. And yet, this advanced technology is already being used for gritty, real world tasks, like manufacturing plant refurbishment and marine retrofitting.

One interesting use has been historical preservation. Across the world, cathedrals, archaeological sites, and other areas important to our heritage are being preserved virtually, to assist in physical preservation.

At Darlington, this urge to preserve has been applied to a piece of living, working history that facilitates speeds of well over 200 mph. Thanks to the accuracy of this evolving technology, it’s possible for the Lady in Black to get a facelift while preserving the qualities that made her beautiful in the first place.


Angus W. Stocking

Angus W. Stocking, L.S., is a licensed land surveyor who now prepares information marketing content for the infrastructure industry.


Angus W. Stocking, L.S.
P.O. Box 872
Paonia CO 81428
270.363.0033 office