Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Reference
GV_HAIR_INTERSECTION_OBJECTParameter: Mode
GV_HAIR_INTERSECTION_MODEParameter: Velocity Mode
GV_HAIR_INTERSECTION_VELOCITY_MODEParameter: Position
GV_HAIR_INTERSECTION_INPUT_POSITIONParameter: Velocity
GV_HAIR_INTERSECTION_INPUT_VELOCITYParameter: Radius
GV_HAIR_INTERSECTION_INPUT_RADIUSParameter: Intersection
GV_HAIR_INTERSECTION_INTERSECTIONParameter: Guide
GV_HAIR_INTERSECTION_GUIDEParameter: Segment
GV_HAIR_INTERSECTION_SEGMENTParameter: Segment Delta
GV_HAIR_INTERSECTION_SEGMENT_TParameter: Ray Delta
GV_HAIR_INTERSECTION_RAY_TParameter: Position
GV_HAIR_INTERSECTION_POSITION