Conversion of wireframe to ACIS solid models for 2 1/2-D engineering components

Abstract

Wireframe models need to be converted to solid models as the latter tend to become more widespread, consistent and affordable. A conversion algorithm for manifold objects was defined to obtain ACIS, thede facto standard B-rep model from a neutral IGES wireframe model and was implemented in C++ in successive stages as follows. All potential surfaces are found first. The entities lying on the same surface are examined in order to form closed profile-loops. Loop nesting is examined according to a ray casting algorithm. Adjacency and nesting of loops is used in order to assign traversal directions to all edges according to the Mobius rule. Invalid profiles (those containing edges belonging to more than two loops) are searched for and successively removed. The final test is that of edge type. If the majority of edges turn out to be concave, the traversal sign of all edges is reversed, so that the body is solid in empty space and not the other way around. For engineering components the algorithm adequately resolves all singular cases.