1. A method for obtaining information about radiation arising from within an environment, the method comprising: providing a directionally sensitive radiation detector which has a field of view; providing a visual image capturing device which has an area of vision; conducting a measurement of the radiation for a field of view, the field of view including a part of the environment; recording the measurement of radiation together with an indication of the spatial position of the respective field of view relative to the detector; obtaining a visual image of an area of vision, the area of vision including the part of the environment within the field of view and recording that image together with an indication of the spatial position of that field of view relative to the detector; and selecting after completion of the measurement of radiation, a set of data from the measurement of radiation according to a criteria, the criteria also being set after completion of the measurements of radiation; and overlaying information from one or more of the measurements of radiation with one of the visual images.