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Capturing sporting events live in 3D

Summary

Drs Allen, Choppin, Goodwill and Prof Haake in the Centre for Sports Engineering Research (CSER) have developed new methods to allow accurate simple and low-cost 3D measurement. These methods have been applied to measure the performance of sports equipment and competitors, both in training scenarios and at actual sporting events. Technology developed for the laboratory was then translated to new in-situ systems that were simpler, more accurate and less costly than previous methods.

This success led to the Centre implementing camera-based analysis systems within numerous Olympic GB training facilities in preparation for London 2012 and Rio 2016, and the implementation of systems at the International Tennis Federation (ITF) to allow them to monitor the game of tennis and set its rules. It has also led to other health and commercial sector innovations.

Our research

The Centre's academics were industrially sponsored to develop an understanding of dynamic tennis shots. Initially they used finite element or Newtonian models and a bespoke impact rig with 3D photogrammetry to measure the complex motion of the racket and ball.

Lab-based studies developed an understanding of dynamic tennis shots using finite element or Newtonian models. These models were validated experimentally using a bespoke impact rig with 3D photogrammetry to measure the complex motion of the racket and ball. The model was also used to look at the effect of tennis racket parameters on simulated ground-strokes before moving to the tennis courts. A novel 3D method of racket and ball tracking using high speed cameras and planar calibration was developed and used during play at Wimbledon qualifiers.

In parallel to this, a method of automatically measuring ball spin during play was developed. The work was used to develop laboratory systems at the ITF to determine the physics of spin generation in tennis using the knowledge of real play conditions. It was determined that friction between strings was much more important than friction between the strings and the ball.

The research marks a transition from lab-based studies to measurement in real environments. Capture of useful 2D and 3D information in the field relies on a robust and practical camera calibration system, for which the planar calibration system was developed. The research demonstrated that planar calibration was superior to Direct Linear Transformation (previously used by most researchers) in many real-life scenarios because reconstruction errors were smaller, the calibration object was simpler to use and errors scaled with the environment.

Following on from this work, the research team explored the potential of using low-cost, off-the-shelf technologies to track and analyse the movements of competitors at sports events. It was discovered that low-cost depth cameras such as the Kinect, which enables video game users to interact with their computer through body movements, was a relatively accurate and easy-to-use option.

Without a doubt, the projects delivered have contributed to the medal success we have seen in London... many of the sports have highlighted the support and the benefits of the numerous projects in partnership with Sheffield Hallam University.

CEO of UK Sport


The impact

The Centre for Sport Engineering Research was appointed as a UK sport Innovation Partner to implement performance analysis technologies in the lead up to London 2012, CSER used the camera and photogrammetric expertise developed in tennis to create calibrated measurement systems for use in day-to-day training and coaching for national teams including GB Boxing, GB Taekwondo and British Gymnastics. Coaches found them simple to use and reported that the automated video analysis they generated contributed to significant GB medal success.

The ITF has implemented much of the Centre's research within its systems for monitoring the nature of the sport. Research on the measurement of spin has been implemented in the software SpinDotor and used at the Davis Cup, the ATP Masters and at Wimbledon. CSER's work allowed the ITF to assess the effect of strings on spin generation by specific rackets. The results showed that spin generated by professional players is significantly less than that of the 'spaghetti racket' which was banned in 1980; the ITF will continually monitor the amount of spin in the game. Prof Haake's expertise in performance analysis systems and experience from UK Sport were used to inform the Technical Commission and the introduction of a new rule to tennis (Rule 31) at its AGM on 12th July 2013. This rule allows the use of performance analysis technology in tournament play for the first time and will come into force on 1st January 2014.

SpinDoctor was sold in collaboration with the ITF to Prince, IsoSport and adidas to use in their labs to measure spin in the field. adidas also requested a further system for measuring football 3D spin vectors and, since 2011, adidas footballs have been tested using this system.

A full suite of applications was made available as open source software to allow the research community to benefit from the enhanced accuracy of the planar method and the low cost abilities of emerging depth cameras.

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