The camera calibration procedures and the tri-dimensional reconstruction of the coordinates were initially proposed by Abdel-Aziz and Karara and are known as Direct Linear Transformation (DLT). The two main systems used for game analysis, in the different sports, are based on video images analysis and GPS technology. Several published works have focused on circuits designed to simulate typical situations of a football game, characterized by movements at different speeds, from walking to maximum speed (sprint), frequently without ball, including quick change of direction. Introduction Since Reilly and Thomas, early study in monitoring football players, the interest and timeliness of this topic has been demonstrated by research conducted by several teams over the last decades.

The validity and the intra-user and inter-users reliability of the methodology used were proved by all the statistical parameters used (the relative technical error of measurement (ETM), the Pearson coefficient (r), and the intra-class correlation coefficient ( ICC)). The coordinates obtained by this methodology were compared to the coordinates obtained by dGPS receiver. The reconstruction of virtual coordinates of the player into real coordinates was carried out using DLT-2D, with algorithms developed in MATLAB’ software routines. In order to obtain the 2D coordinates of the movements of a player from the virtual coordinates, the TACTO software was used twice, first for calibration (the virtual coordinates of a set of reference points at the game surface were collected, corresponding to points with known real coordinates) and then for digitalization (reconstruction of coordinates). Abstract The aim of this study was to present a validation protocol using a global positioning system with real-time differential correction (dGPS) to assess the validity and the reliability of a semi-auto tracking software (TACTO) used to quantify the movement patterns of football players.

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