VIDEO MEASUREMENT OF LINEAR DISPLACEMENT ALONG AN OBLIQUE LINE USING THE CROSS-RATIO

Authors

  • Mark Colpus
  • Mark Goss-Sampson

Keywords:

cross-ratio, camera, calibration, perspective

Abstract

The purpose of this study was to rediscover the cross-ratio and assess its effectiveness for measuring linear displacement when the image plane is not parallel to the object plane. In the laboratory a fixed, 4m object length was reconstructed with a mean absolute error of 2.6mm (s.d. = 1.6mm, maximum = 4.9mm). In the field, two cameras filmed a fixed, 8m object length with a mean absolute error of 13mm (s.d. = 5mm, maximum = 20mm). The method is very accessible to non-specialists in projective geometry and the results are both valid and reliable.

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Published

2016-05-05

Issue

33 International Conference of Biomechanics in Sports (2015)

Section

Methodology

License

Authors can retain copyright, while granting the International Society of Biomechanics in Sports (ISBS) the right of first publication.