Method used

Juiz Virtual makes use of image-based modeling techniques. The goalposts and points on the field have a relative position determined by football rules. When they are associated to the corresponding points on the image, it is possible to determine the camera's position and orientation. This information then allows the location of the ball's and players' position on the field from their position on the image. Once the three-dimensional model is constructed, it is possible to place the camera in any arbitrary position.
A crucial point is the determination (or calibration) of the camera. Juiz Virtual uses a two-step calibration method which employs linear models of least squares.
More details can be obtained in the following article and PowerPoint presentation.

Carvalho, P. C. P., Szenberg, F., and Gattass, M. Image-based Modeling Using a Two-step Camera Calibration Method. SIBGRAPI'98 (doc (Word97) ou ps format).
Juiz Virtual: uma aplicação de modelagem baseada em imagens [Juiz Virtual: An Image-based Modeling Application] (ppt format).

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