2011

Draw Construction Lines (and Rays)
Lines that extend to infinity in one or both directions, known as rays and
construction lines, respectively, can be used as references for creating other
objects.
For example, you can use construction lines to find the center of a triangle,
prepare multiple views of the same item, or create temporary intersections to
use for object snaps.
Infinite lines do not change the total area of the drawing. Therefore, their
infinite dimensions have no effect on zooming or viewpoints, and they are
ignored by commands that display the drawing extents. You can move, rotate,
and copy infinite lines just as you can move, rotate, and copy other objects.
You may want to create infinite lines on a construction line layer that can be
frozen or turned off before plotting.
Construction Lines
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.
■ Horizontal and Vertical. Create construction lines that pass through a point
you specify and are parallel to the X or Y axis of the current UCS.
■ Angle. Creates a construction line in one of two ways. Either you select a
reference line and then specify the angle of the construction line from
that line, or you create a construction line at a specific angle to the
horizontal axis by specifying an angle and then a point through which
the construction line should pass.
■ Bisector. Creates a construction line that bisects an angle you specify. You
specify the vertex and the lines that create the angle.
■ Offset. 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.
Rays
A ray is a line in three-dimensional space that starts at a point you specify and
extends to infinity. Unlike construction lines, which extend in two directions,
510 | Chapter 16 Draw Geometric Objects