All interactive tools and some other processing methods allow to select geometrical shapes on data with mouse: points, lines, rectangles, circles/ellipses. Existing selections can be similarly modified by dragging corners, endpoints, or complete selections. When mouse cursor is moved near to an editable point of a selection, is changes its shape to indicate the possibility to edit this point.

Each tool generally uses only one type of selection and when it is activated on a data window, it sets the selection mode to this type. Selections of other types than currently displayed are remembered and they are recalled when a tool which uses them is activated again. E.g. when you select several lines with Profile extraction tool, then switch to Statistical quantities (the lines disappear) and select a rectangular area to calculate statistical characteristics of, and then switch back to Profile extraction, the rectangle disappears and the lines appear again.

Tools that use the same type of selection – e.g. both Statistical functions and Statistical quantities use rectangular selection – share it. To calculate height distribution of the same rectangle you have selected for statistical quantities, it is sufficient to switch the tool.

Figure 3.9.  Data window with three selected lines, two horizontal and one vertical.

If you save data in Gwyddion native file format (.gwy), all selections are saved together with data and recalled the next time the file is opened and appropriate tool chosen.

Pressing Shift during selection restricts the degrees of freedom of the shape, making it easier to draw shapes form a specific subset. E.g. pressing Shift restricts rectanglular selections to perfect squares, or it restricts line directions to multiples of 15° in line selections.