Construct a segment between two points. The points do not need to exist, they will be constructed, as soon as
you click on an empty spot.
Construct a segment. You also need to points for that.
Construct a triangle. You need three points for that.
Construct a vector. A vector is segment with a direction. You need a vector to move a point.
Construct a ray.
Constrcut a parallel line. You need to click on an existing line and then choose a point through which
the parallel line should run.
Constrcut a perpendicular line. You need to click on an existing line and then choose a point through which
the perpendicular line should run.
