为了更好地理解三维景物，介绍了前人对线画图标记的研究成果，同时建立了一种标记具有相切面的曲面立体线画图的方法，并给出了具有相切面的曲面立体线画图的标记规则。由于线画图中的节点是由三面角构成的顶点的投影，因此对于画出隐藏线的具有相切面的曲面立体线画图，其合法的节点标记形式有38种，其中Y型节点有6种，W型节点有18种，V型节点有14种。新的标记方法适用于由平面立体和曲面立体组合而成的复杂立体线画图。

Although line drawings consist of only line segments on a plane, they convey much information about the three-dimensional object structures. For a computer interpreting line drawings, some intelligent mechanism is required to extract three-dimensional information from the two-dimensional line drawings. The labels of the line drawing as an efficient aidded method is take part in recovering the 3-D scene the line drawing. Many impossible configuration can be exclude by consistent labeling.In this paper, according to current the theory of labeling ,a new labeling method for the line drawing of an object with tangent curve surface is proposed. The labeling rules are established. The natural line drawings can be labeled correctly by using of our labeling method. There are 38 kinds of possible junctions for a hidden-part-draw natural line drawing that is the projection of a three-dimensional object with tangent curve surface, in which there are 6 possible Y junctions, 18 possible W junctions, 14 possible V junctions. The labeling method is efficient to the line drawing of a complex object consisting of polyhedrons and objects with curved surfaces.