While attraction mode provides coincidence of boundaries of the neighboring features during their building, the capture mode permits the user to keep this coincidence when changing features in the course of editing.
The capture mode is turned on by the checkbox Capture in the lower part of the window “Editor control” (see figure 17-2). In the field Radius located on the right of this checkbox the value for capture radius is set.
If position of vertices of some feature is changed when the capture mode is turned on (when moving of either one or several vertices or a feature as a whole is performed), the system checks if some vertices of other features are located within the capture radius from one of the moved vertices. If there are such vertices, they are “captured”, that is, attracted to the closest of the vertices being moved, and are moved together with it.
If there are no vertices of another feature but there are internal points of some edge in the capture radius, splitting of this edge occurs and the vertices formed after the edge split are captured.
Operation of capture is performed only in the case if the distance to which the vertices are moved does not exceed some capture threshold. The value for this threshold is calculated by multiplying the map range by the coefficient specified on the page of editor settings (see “Parameters of editor settings”). Capture is not performed if the distance to which vertices are moved is too big.
As it is follows from the description, the capture operation not only keeps the existing coincidence of vertices and edges of different features, but can be also used for setting new coincidences in the range of capture radius similarly to the attraction mode. If it is desirable to avoid such an effect it is required to set a very small value for the capture radius, though it should be greater than zero. If this radius is smaller than the minimal distance between non-neighboring features then the capture action will affect only the coincident vertices and edges of the features neighboring with the moved one.
For preliminary evaluation of capture possibility one can use the mode of capture radius visualization. In this mode when editing vertices of a line or area feature in interactive mode, a dotted circle with the radius equal to the capture radius is displayed around the cursor. Capture will be performed if when moving a feature vertex some other vertex of another feature (or part of its edge) falls into a dotted circle.
The mode of capture radius visualization is turned on by default. It is possible to switch it off changing the corresponding parameter of the editor settings (see “Parameters of editor settings”).
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