Extracting Topological Relationships from Wire-Frame CAD Model

Abstract

This paper presents an algorithm for extracting topological relationships from a wire-frame computer-aided design (CAD) model of a given concrete floor. The algorithm consists of three stages. The first stage processes the wire-frame CAD data to differentiate between the interior and the exterior of a given floor configuration and to identify obstacles. The second stage employs the plane sweep paradigm to obtain all interior beam to beam intersection points. The third stage partitions the interior of the given floor into rectangular slabs (face entities). Information regarding the location and dimensions of concrete columns are also obtained using a range-searching technique and is stored along with the partitioning information. Plane sweeps are performed in two principal directions to extract adjacency relationships among the partitioning rectangles. The adjacency relationships are stored in a graph, called the rectangle adjacency graph (RAG), similar to the face adjacency graph (FAG) commonly used in boundary representation (B-Rep) models. The RAG can be used as a complete information model for computer-aided generation of: (1) A construction process plan; and (2) a detailed path plan for computer numerically controlled (CNC) concrete placement. The algorithm is applicable to concrete floors designed using one- and two-way slab theories that guarantee orthogonal polygon shaped floor boundaries and interior obstacles.