Streamlining BIM models for GIS integration: an advanced approach to building envelope extraction

Building Information Modelling (BIM) models are crucial for urban building modeling in three-dimensional (3D) Geographic Information Systems (GIS); however, their intricate nature requires lightweight design for seamless GIS integration. Envelope extraction is a primary method for achieving lightweight BIM; nevertheless, it encounters challenges related to robustness and simplification. To tackle this issue, this study proposes a more effective envelope extraction method. Initially, BIM elements are categorized into three types based on their semantics: space-occupying, portal, and other facility elements. Subsequently, for space-occupying elements, a 3D alpha wrapping algorithm is employed to obtain a tightly enveloped triangular mesh and then simplified into a lightweight polygonal mesh. Finally, portal elements are replaced with simplified proxies and embedded into a polygonal mesh through extrusion operations to refine the model. The refined model is combined with other facility elements to achieve the final simplification result. Experiments were conducted using publicly available datasets and manually created BIM models of various types and complexities. The experimental results demonstrate that our method significantly reduces the data volume of BIM models while maintaining their accuracy. Furthermore, this approach does not necessitate strict geometric requirements for BIM building elements and allows for gaps between them, thereby exhibiting higher robustness.