If the two level 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。
The two picture 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。
Take high level semantic information and low level picture visual characters as design patent characters, the two kinds of information cut down each other's shortage.
特征提取采用底层信息和高层语意相结合的方法，弥补了相互的不足；
Take high level semantic information and low level picture visual characters as design patent characters, the two kinds of information cut down each other's shortage.
特征提取采用底层信息和高层语意相结合的方法，弥补了相互的不足；
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