Abstract
In this paper the author suggests a drawing method to discriminate between the developable surface and the skew surface.
The surface of the curved levee is a ruled surface of which the director is the levee normal line. The generator of the slope is the batter board. The gradient of the batter board is much steeper than the gradient of the director. So the surface of the curved levee is not the convolute of the levee normal line.
The developable surface has the generator: (1) parallel to each other, (2) concurrent with a point, and (3) tangent to a space curve. So drawing the projection of the generator, the developable surface can be dis-criminated.
Three types of the curved levee were discriminated. The first was a skew surface, the second was a part of a convolute of an other helix, and the third was a part of a cone.
