Abstract: A system for measurement of spatial coordinates and/or orientation of a probe, comprising a first spatial direction sensor associated with a pattern of targets with known positions relative to each other and to the first spatial direction sensor, a second spatial direction sensor, and processing means for the computation of the orientation and/or spatial coordinates of the pattern of targets relative to the second spatial direction sensor based on the known positions of the targets relative to each other and a determination of the spatial directions of the targets with respect to the second spatial direction sensor, wherein at least three of the targets are in the field of view (FOV2) of the second spatial direction sensor irrespective of the orientation of the pattern of targets and wherein the first spatial direction sensor determines the spatial coordinates and/or orientation of the probe.