Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Reference
GV_HAIR_COLLISION_OBJECT
Parameter: Collision Index
GV_HAIR_COLLISION_INPUT_NUM
Parameter: Count
GV_HAIR_COLLISION_OUTPUT_COUNT
Parameter: Guide
GV_HAIR_COLLISION_OUTPUT_GID
Parameter: Segment
GV_HAIR_COLLISION_OUTPUT_SID
Parameter: Segment Delta
GV_HAIR_COLLISION_OUTPUT_SEG_DELTA
Parameter: Polygon Index
GV_HAIR_COLLISION_OUTPUT_POLYINDEX
Parameter: Hit Point
GV_HAIR_COLLISION_OUTPUT_HITPOINT
Parameter: Velocity In
GV_HAIR_COLLISION_OUTPUT_VELOCITY_IN
Parameter: Velocity Out
GV_HAIR_COLLISION_OUTPUT_VELOCITY_OUT
Parameter: Frame Delta
GV_HAIR_COLLISION_OUTPUT_FRAME_DELTA