154 4 Surfaces of Gaussian curvature zero
E1
E3
E2
Fig. 4.1. Ruled surface of type circular cone C
2
R cos Φ 0 , directrix: parallel circle S
1
R cos Φ 0 , generating vector
field C Φ (Λ, Φ 0 ).
Fig. 4.2. Helicoid as ruled surface, one-sheeted hyberboloid of revolution as ruled surface.
E1
E3
E2
Fig. 4.1. Ruled surface of type circular cone C
2
R cos Φ 0 , directrix: parallel circle S
1
R cos Φ 0 , generating vector
field C Φ (Λ, Φ 0 ).
Fig. 4.2. Helicoid as ruled surface, one-sheeted hyberboloid of revolution as ruled surface.