The invention belongs to the related technical field of
computer aided design, and particularly discloses a CAD geometric constraint
system diagram expression method and
system based on a ternary body,
CAD system expression is divided into three
layers, the top layer is geometric elements and
engineering constraints; the middle layer adopts a ternary body which comprises a position body representing the positions of the geometric elements, a posture body representing the postures of the geometric elements, and a parameter body representing the measurement of the geometric elements or between the geometric elements; the geometric constraint
directed graph of the bottom layer comprises graph vertexes and directed edges, the graph vertexes comprise five types: cube vertexes corresponding to a position body, sphere vertexes corresponding to an attitude body, and parameter vertexes or constrained vertexes corresponding to a parameter body, and the whole can be used as a composite vertex when the subgraphs of the
directed graph are subjected to overall analysis or non-constrained vertexes form a directed ring; and the directed arc records the
constraint relation between the vertexes of the graph. According to the method, two-dimensional and three-dimensional
engineering constraints and geometric elements are uniformly expressed, the geometric elements are decomposed more thoroughly, and the solving scale is effectively reduced.