For the proper understanding and modelling of pedestrian dynamics, reliable empirical data are necessary. Trajectories of every person with a high temporal and spatial resolution allow a detailed analysis of movement as well as the calibration and verification of microscopic models in space and time.To extract individual trajectories on a microscopic level different techniques have been developed de- pending on miscellaneous requirements. In this paper we analyse how the quality of quantities like velocity or density depend on the technique chosen to track pedestrians. For this purpose, errors due to perspective distortion, use of markers, type of markers, and other conditions will be scrutinized.It turns out that the usage of imaging systems like cameras give currently the best results and that marker particularly structured marker for detecting a person in a crowd obtain the most accurate trajectory especially if the height of the person is coded by the marker or the distance to the camera is measured otherwise. To minimize the errors resulting from the perspective view a small angle of view and thus high mounted cameras should be used for capturing the whole area of interest. The small angle of view also decreases the risk of occlusion and lens systems for large focal lengths usually have a smaller optical distortion error
