All commands which operate on data elements may be limited as to the range of data elements upon which they act. The region or ``window'' over which operations take place is referred to as the ``Region Of Interest'' (ROI) or the ``Active Data Region''(ADR). In other programs and contexts this concept is sometimes referred to as a ``Data Window''.
(Note: Originally I used the term ``active data region'' (ADR), as this more precisely describes the concept, however, since then the term ``region of interest'' (ROI) has become generally used for the same or similar concept. Thus, this term is now used within FIT2D and documentation. Unfortunely the acronym ``ROI'' is now also commomly used for ``Return of Investment''.)
When data is input the ROI is initially set to include all the data. The menu commands ZOOM IN, UN-ZOOM, and FULL buttons allow the ROI to be changed (see Section 4.2.3). The MOVEMENT graphics sub-menu also contains many commands which change the ROI e.g. all the commands which move around the image; UP, DOWN, LEFT, etc.
It should be noted that the ROI concept does not just affect graphical display, but also affects arithmetic and other operations, and the output of data to file (OUTPUT). FIT2D follows the WYSIWYG (``what you see is what you get'') principle in data operations, so only the area of the data which is currently displayed will be operated upon. (The exception is the EXCHANGE command which swaps the entire data-sets including the definitions of the ROI.)