For adding a line feature in the mode of coordinate editing the menu item Object+Add should be performed and line spatial category should be selected from the opened nested menu. A dialog box of adding a line feature shown at figure 17-6 will be opened.
Figure 17-6. Adding a line feature
Selection of a layer and feature type is performed as when adding a point feature.
To create a line feature it is required to specify coordinates of vertices of the polyline which determines this feature.
Below the pane of layer and type selection there is a pane of list of vertices. It contains a numbered list of polyline vertices. In every row there are point coordinates, length of the edge connecting the present vertex with the next one and slope angle of this edge towards the horizontal axis.
Still lower you will find the pane of vertex coordinates.
To add a new polyline vertex, it is required to enter its coordinates in the fields X and Y in the input pane and then push the button Add. The row with coordinates of the new vertex will be added before the selected row of the pane of list of vertices. If it is necessary to add a new vertex between two polyline vertices added earlier, one should select from the list the vertex before which the new vertex should be inserted, enter its coordinates and push the button Add. If you need to add the vertex at the end of the list, an empty row at the end of the list should be selected.
In the fields Distance and Angle of the pane From previous vertex the values for the vertex with coordinates X and Y are calculated with respect to the previous vertex from the list (to be more exact, with respect to the vertex lying one row above the selected vertex in the list).
To change coordinates of any polyline vertex it is required to select the corresponding row of the list, specify correct values in the pane of entering coordinates and push the button Change.
The button Edit transfers coordinate values from the selected vertex of the list to the fields of the pane of vertex coordinates. In these fields the values can be corrected and then transferred back to the list using the button Change.
The button Remove removes the selected vertex from the list.
The button Reverse causes changing of the order of vertices in the list to the reverse one (the first vertex becomes the last and vice versa). The order of vertices can be important if the type of the line used for displaying the present feature is not symmetrical, that is, the right line side differs from the left one.
Fields of the pane From previous vertex provide the user with another possibility of specifying the position of the vertex being added – not in the form of absolute coordinates, but with respect to the previous vertex. It is possible to enter these values in the fields Distance and Angle, then the coordinate values for the vertex located at a given distance and direction from the previous vertex in the list will be calculated in the fields X and Y.
The button Circle enables the user to automatically build coordinates of a set of points which roughly form an opened circle and include them into the vertex list. A dialog box “Creating circle” shown at figure 17-7 will be opened.
Figure 17-7. Dialog box “Creating circle”
In the fields of this dialog box the user can specify parameters of the regular polygon which imitates a circle: center coordinates, radius and the number of polygon vertices. By default the system offers to use 36 vertices. After pushing the button Perform the list of vertices is cleared and coordinates of polygon vertices are entered into it, starting from the upper one in counter-clockwise direction. The last created vertex is not connected to the first one, that is, the circle remains opened.
If at the moment of pushing the button Circle there were not less than two points in the list of vertices, the opening dialog box has the title “Transforming to circle” and its fields are automatically filled with values calculated on the basis of coordinates of the vertices from the list. The system offers the arithmetic average of the corresponding coordinates of vertices from the list as coordinates of circle center, and the arithmetic average of distances of these vertices from the calculated center – as a radius.
After creating the circle, the user can continue adding line feature vertices in the usual way.
After performing adding of all polyline vertices (not less than two) creation of the line feature is completed on pushing the button OK.
 |  |
