1. A method for determining the extension of a trajectory in a space-time volume of measure images said space-time volume of measure-images being generated by a measuring method utilizing a measuring system comprising a first light source and a sensor, said measuring method comprises a step of, in a predetermined operating condition of said measuring system, moving a measure object along a first direction of movement in relation to said measuring system while said first light source illuminates said measure object whereby said sensor generates a measure image of said measure object at each time instant in a set of at least two subsequent time instants, thus generating said space-time volume of measure images wherein a feature point of said measure object maps to a trajectory in said space-time volume, wherein said method for determining said extension, in said predetermined operating condition of said measuring system, comprises the steps of: moving a reference object along said first direction of movement in relation to said measuring system while illuminating said reference object with incident light whereby said sensor generates a reference image of said reference object at each time instant in a set of at least two subsequent time instants, and determining said extension based on said reference images.