|  |  | Polylines

## Polylines

Polylines have a datum and a position format for all its points, a colour and a width (in pixels) used in displaying it on the map.

A map background image name can be given for each polyline, so that when the polyline is displayed on the map window the named image is automatically loaded if the map is empty. See below for the details.

Changing the position format to grid coordinates may produce the following effects:

- the polyline datum is changed to the datum required by the grid
- some/all positions are shown as undefined (either `-- 0 0` or `-- 0`) if they are out of the scope of the grid; this however will not affect the internal representation of the position and a change to a suitable format will yield correct values. When reading a polyline from a file, positions may also be shown as undefined in which case the position format should be changed.

Each polyline point has a position and, possibly, its altitude in either metres or feet, depending on the existing option for this. A point can be changed by double-clicking on the corresponding line in the list of points of the polyline edit window.

A polyline can be subdivided into segments and the segments will be drawn unconnected when the polyline is displayed on the map. The first point always starts a segment, and any other point can be marked as a segment starter from the polyline edit window by using the mouse right-button on the last column of the points list.

A polyline can be created from a track : see above.

A polyline can be created by drawing on the map as explained below.

The edit window for polylines allows some operations on polylines that may be useful to clean uninteresting start or end parts, or to compose a single polyline from others. They are:

- "Chop head": all polyline points from the first to and including the first one selected are deleted; if there is no selection the first point is deleted;
- "Chop tail": all points from and including the last one selected to the last are deleted; if there is no selection the last point is deleted;
- "Include before", or "Append": the points of a polyline are put before the first, or after the last point;
- "Loop": a copy of the first point is added to the end of the polyline;
- "Delete": deletes all the selected points;
- "Clear": deletes all points.

A polyline can be splitted by taking either each selected point or segment starter as the first point of a new line extending up to and excluding the next such point. Lines with at least two points obtained in this way are created, as well as a group with all of them. These new lines inherit the datum, the position format, segments (unless when splitting by segment starters), width, colour and map background of the original line. They and the new group get names generated automatically. The original line is not affected by this operation.

A polyline can be converted into a track from the polyline window, keeping the information on segments.

|  |  | Polylines