Three main reference systems are used for
the detector elements description :
MAster Reference System - MARS :
origin is in the
target center, beam direction
along Z axis, vertical line along Y axis.
Sector Reference System
is connected with one
sector of CLAS with the origin in the
target center.
A (X,Z) plane divides the
Sector in two symmetric parts.
This plane is named Sector middle plane
or middle plane.
The Z axis is
parallel to the Z axis of the MAster Reference
System.
Segment Reference System is
connected with each CC segment.
The origin is in the target center, the Y axis
lies in the Sector middle plane and
crosses the target
and the center of the CC segment.
The X axis is perpendicular to the middle plane.
A (X,Y) plane crosses the centers of the
mirrors and the Winston Cones,
and is called the Segment median plane
or Median plane.
This reference system is convenient for the description
of mirror shapes
and for the ray-tracing inside the segment.
