Computer Graphics World

Edition 2 2018

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e d i t i o n 2 , 2 0 1 8 | c g w 3 1 Nexus soware. Once the team knew where everything was going, they still needed to be able to get in and out quickly and efficiently. According to Pearsall, the process was similar to a pit crew team in motor car racing. "Ice time is costly. We can't leave the cameras set up permanent- ly, so we have to set up, test, and take everything down within three to four hours," says Pearsall. "Everyone knows their jobs. We've got it down to a fine art." Hitting the Ice The first on-ice study conducted by the IHRG compared the skating start biomechanics of male ice hockey players with different levels of skill and experience. Since then, the IHRG has completed and published a second study, authored by Jaymee Shell, a master's graduate student at McGill University at the time. Shell studied the biomechanical differences between male and female players. As with other sports analyses, the motivation was to better understand the optimal movement techniques for skating perfor- mance, as well as to identify potential factors that may be implicat- ed in lower body injuries. "As reported in prior running research, frontal plane differences between genders in hip and knee movements exist," say Shell. "So, we wanted to look at male and female ice hockey players and see if similar lower body kinematic differences existed or were greater." The indoor ice rink's cold temperatures and high humidity were challenging for the cameras. There was the fear that the reflection from the ice would obscure marker tracking, but the equipment had no issues. The study represents a major achievement in 3D mo- cap, as the team was able to expand its range and calibrate a large 15x3x2-meter (50x10x6.5-foot) capture volume on the ice to record skating kinetics, with high intra-trial reliability. They did run into an issue, but the team was able to turn to Vicon application engineer John Porter, who Shell says, "saved her project." "It wasn't the camera's fault at all – the cameras did exactly what they had to do," Shell says. "But having the Vicon support through the study was really invaluable. I can't praise the support team enough for what they did. I might still be labeling my data if it weren't for them!" Following Shell's study and the results it produced, the IHRG decided to incorporate some of her methods and include female athletes in more of its studies. Speeding Ahead Soon aer Shell completed her study, the IHRG upgraded its system to include a Vantage and Vero optical camera, bringing the total number of cameras to 18. Soon aer the upgrade, the IHRG expand- ed its studies to include puck shots, which brought with it the added risk of a puck bouncing back and hitting a camera. To compensate, the target nets were placed far enough back out of the capture area to reduce the risk of any collisions. The team later added a Bonita camera alongside the Vantage to overlay the video with stick figure motions, making it easier to com- municate their findings with others. EMG and force sensors were later introduced, all synchronized through Vicon soware. "To date, we've achieved a 15-meter (50-foot) FOV over the ice surface," Pearsall explains. "In skating, when you're at full speed, you can do 15 meters in two strides. As well, the increased pixel count and resolution of the Vantage cameras helps maintain the resolution needed to track the full-body marker set." The IHRG's success has also led to studies into other fields beyond hockey, including working with groups to better understand how footwear performs on snow and ice. With the help of the Vicon cameras, the team is able to collect more data than ever before, which could prove to be invaluable to people who consider the ice a second home.

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