The reference orbit consists of a series of straight line segments and circular arcs. It is defined under the assumption that all elements are perfectly aligned. The accompanying tripod of the reference orbit spans a local curvilinear right handed coordinate system (x,y,s) The local s-axis is the tangent to the reference orbit. The two other axes are perpendicular to the reference orbit and are labelled x (in the bend plane) and y (perpendicular to the bend plane).
Figure 1: Local Reference System