Data can be selected to lie within either a circular or annular region around a user defined central point. The user is asked which type of 'aperture' is required (Annular or circular), the (X,Y) coords of the central position, the outer radius of the region (for a circular region this is just the radius of the 'aperture') and, for an annular aperture, the inner radius. The units used are those of the X and Y LISTs in the event dataset.
Subtopics: