A construction line can be placed anywhere in three-dimensional space. You can specify its orientation in several ways. The default method for creating the line is the two-point method: you specify two points to define the orientation. The first point, the root, is the conceptual midpoint of the construction line, that is, the point snapped to by the Midpoint object snap.
You can also create construction lines in several other ways.
The horizontal and vertical methods create construction lines that pass through a point you specify and are parallel to the X or Y axis of the current UCS.
The angle method creates a construction line in one of two ways:
Select a reference line and then specify the angle of the construction line from that line.
Create a construction line at a specific angle to the horizontal axis by specifying an angle and then specifying a point through which the construction line should pass.
The bisector method creates a construction line that bisects an angle you specify. You specify the vertex and the lines that create the angle.
The offset method creates a construction line parallel to a baseline you specify. You specify the offset distance, select the baseline, and then indicate on which side of the baseline to locate the construction line.
