Individual segment along the IfcAlignmentHorizontal, being defined in the x/y coordinate space. Each single horizontal alignment segment has an optional associated segment definition. The placement of IfcAlignmentHorizontalSegment and the IfcCurveSegment StartPlacement correspond to each other. 

The following information can be calculated (and is therefore not exchanged explicitly to avoid redundancy and inconsistencies):

• the end point (from start point, direction, segment length and curve parameter)
• the start distance along (from the end distance along of the previous segment, or the start distance along of the horizontal alignment (if it is the first segment)
• the end distance along (from the start distance and the segment length)
• the end direction (from the curve parameter, the start direction and the segment length)
• the point of intersection (from the start direction and the end direction)

The following checks can be done to validate the correct exchange:

• continuity – whether the calculated end point of the previous segment matches with the provided start point of this segment
• tangential continuity – whether the calculated end direction of the previous segment matches with the provided start direction of this segment