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Sports Engineering

, Volume 17, Issue 2, pp 97–102 | Cite as

The effect of light reflections from the snow on kinematic data collected using stereo-photogrammetry with passive markers

  • Niels Jensby Nedergaard
  • Frederik Heinen
  • Simon Sloth
  • Kim Hébert-Losier
  • Hans-Christer Holmberg
  • Uwe G. KerstingEmail author
Technical Note

Abstract

This study aimed to compare kinematic data collected during ski-cross starts outdoors on snow in daylight (high albedo) to similar data collected indoors with infiltrating sunlight but without light reflections from the snow (low albedo) using a video-based motion capture system with the active filtering function enabled. A 12-camera 3D motion capture system (Qualisys AB, Sweden) was used to measure test objects and eight skiers performing a ski-cross start on a slope outdoors and on a wooden start ramp indoors. The average residuals and standard deviations of the length of the calibration wand calculated indoors and outdoors by the calibration software were compared using descriptive statistics. Static and moving fixed length measures and thigh length measures were compared using Bland–Altman plots. Calibration residuals were slightly increased outdoors (1.77 mm) compared to indoors (1.54 mm), while wand length varied by 3.63 and 1.51 mm, respectively. Fixed static lengths differed by −8.65 ± 4.94 mm (shorter indoors), whereas fixed moving lengths differed by 0.85 ± 1.05 mm (longer indoors). A randomly chosen marker pair on one segment (Thigh) showed a mean difference of 1.19 ± 22.05 mm (longer indoors). It is concluded that 3D motion capture outdoors on snow in daylight is feasible, provides kinematic data comparable to indoors, and could be used to research biomechanics in snow sports.

Keywords

Active filtering 3D motion capture system Outdoor Ski-cross Snow 

Notes

Acknowledgments

We thank Mr. Tommy Eliasson, Sports Director of the Swedish ski-cross national team, for his cooperation during the study and Mr. Mikael Therell, Technician at Swedish Winter Sports Research Centre, for his assistance in building the indoor start ramp. We also acknowledge Mr. Leif Jepsen and Mr. Jan Stavnshøj, Aalborg University, for their assistance with the instrumentation of the start gate. Our gratitude is extended to the team at Qualisys AB for their logistic support and provision of additional cameras and, in particular, Mr. Patrik Almstrøm and Mr. Reimund Trost for their technical help during the testing sessions.

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Copyright information

© International Sports Engineering Association 2013

Authors and Affiliations

  • Niels Jensby Nedergaard
    • 1
  • Frederik Heinen
    • 1
  • Simon Sloth
    • 1
  • Kim Hébert-Losier
    • 2
  • Hans-Christer Holmberg
    • 2
  • Uwe G. Kersting
    • 1
    • 2
    Email author
  1. 1.Department of Health Science and Technology, Center for Sensory-Motor InteractionAalborg UniversityAalborgDenmark
  2. 2.Department of Health Sciences, Swedish Winter Sports Research CenterMid Sweden UniversityÖstersundSweden

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