Linear groups represent a linear
collection of objects and can be used to display, for example,
all the repeaters between two line termination network elements.
The shape of a linear group is defined by the class
IlpPolyline. This class describes an open
polyline made up of an array of points.
When alarms or secondary states are
displayed on a linear group, an information cluster appears at
the center of its median segment. The median segment is the
segment containing the midpoint of the shape.