If the twolevel curves are tangent to each other that means they have the same tangent line. That means that the normal vectors should be parallel. Let me maybe draw a picture here.
如果两个等高线相切，说明它们的切线相同，也就是说他们的法向量应该平行，我再在这里画个图。
2
The twopicture is not quite level that one is higher than the other.
这两幅画挂得不一般高，这幅比那幅高。
3
Take high level semantic information and low levelpicture visual characters as design patent characters, the two kinds of information cut down each other's shortage.