Future industrial and consumer services will more strongly rely on positioning. In addition, positioning provides the potential to create new applications, e.g. gaming in physical environments. Authors of these applications need to assess the availability and the quality of localization signals at the side. For this purpose, we present the concepts and implementation of an environmental scanner, which is initially based on GPS. In a wider sense, it can be applied to evaluate influences of space weather effects to GPS quality and to indicate multipath scenarios. Besides the system architecture and the firmware, particular attention
is paid to pre-processing, visualization, and underlying metrics. A practical difficulty concerns the illustration of a spot on a map, since the error of the estimation of the current position depends on the signal quality. We solve this problem with a novel concept, which considers the size of each spot with the help of various indicators. Moreover, a technique is described to eliminate ambiguities in the case of overlapping of several spots.