geometry
POLYGON Z ((30 10 40, 40 40 80, 20 40 60, 10 20 30, 30 10 40))
POLYGON Z ((35 10 45, 45 45 90, 15 40 55, 10 20 30, 35 10 45), (20 30 50, 35 35 70, 30 20 50, 20 30 50))

POLYGON Z EMPTY