These modes (buttons 
, 
, 
and 
accordingly) enable the user to select or deselect a set of features located in some map area, particularly in the specified rectangular, circle or polygone or the features intersecting the specified polyline (broken line). When turning on one of these modes, the system allows specifying the corresponding figure on the screen.
As an example, selection by polygone can be examined. When selecting this mode the system opens a window “Selection region” with the data about performing selection process. This window is very similar to the window “Ruler” (figure 12-8). It contains coordinates of vertices of the specified polygone and the current cursor position, length of built edges, side slope angle, the current polygone area. The box Autocomplete is always checked since a polygon, not a polyline is built. The window “Selection region” is closed automatically when any other mode is turned on.
To specify a polygon it is required to place the cursor in the position on one of the vertices and click the left button, then specify the second vertex and subsequent ones in the same way. For adding coordinates of vertices from the keyboard it is also possible to use the command Add from the context menu. The system displays built polygone edges by a thick line, a thin line connects the cursor with the first and last built vertices. At figure 13-1 selection by polygone is illustrated. Unsuccessful vertex selection can be canceled by performing the command Rollback form the context menu. For completing building the polygon a double click the last vertex should be performed.
Figure 13-1. Performing selection by polygon
The keys Ctrl, Alt, Shift and a combination <Ctrl+Alt> enable selection or deselection of features by several polygons, and also combining selection by polygon with selection by rectangle, circle, polyline and selection of individual features.
Selection by polyline is performed exactly the same as the one by polygon, but the system does not complete the built polyline, that is, it does not connect the last point with initial one. For selection by circle it is required to select the necessary mode, put the cursor in the circle center, click the left button and then, while holding down the button move the cursor until the necessary radius is achieved. Specifying a circle is completed when the button is released. For selection by rectangle the button should be clicked in one corner of the rectangle and released in the opposite corner.
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