Horizontal Alignment - is defined by Intersection Points (IPs) connected by tangents; optional curves may smooth the transition between tangents. Sometimes the term Point of Intersection (PI) is used; we will often just refer to Plan Points. There is no elevation information associated with the Horizontal Alignment.
Vertical Alignment - is defined by Vertical Intersection Points (VIPs) connected by tangents; optional parabolic curves may smooth the transition between tangents. Sometimes the term Vertical Point of Intersection (VPI) is used; we will often just refer to Profile Points. The Vertical Alignment is defined only by Station (distance along Horizontal Alignment) and Elevation coordinates.
See the following for more information on working with alignments:
