Semi-automatic techniques for as-built BIM façade modeling of historic buildings

This paper presents two new developments for asbuilt BIM modeling of historical buildings. The first is a new library of interactive parametric objects designed for modeling classical architectural elements from survey data. These library objects are dynamic and have parameters that can alter the shape and size of objects for multiple uses and not just once off static modeling. The parametric architectural objects have been designed from historic manuscripts and architectural pattern books. These parametric objects were built using an embedded programming language within the ArchiCAD BIM software called Geometric Description Language (GDL). The second development which is described in more detail in this paper is a parametric building façade which has been developed as a template for fast and efficient modeling of endless configurations of building façades. The design of this parametric façade incorporates concepts from procedural modeling which is an automated approach to generating 3D geometries based on rules and algorithms. With this developed parametric façade, the structure of a façade can be automatically generated by altering parameters for the number of stories, number or horizontal tiles and door position. When automatically generating a façade, the initial position and size of elements are estimated using classical architectural proportions. After the façade is automatically generated users can then interactively edit the position, size and other parameters of façade elements to accurately map objects to survey data. Parametric library objects such as windows, ashlar block wall detail and other architectural elements are incorporated into the parametric façade. The parametric façade template has also been implemented with the Geometric Description Language for ArchiCAD BIM software. This enables the tools developed to utilize the full benefits of BIM software which includes automated construction or conservation documents, semantic object orientated objects based on IFC semantic classes, automatic lists of objects and material and the ability to add and link additional information to the model. Initial tests have shown that the parametric façade is more efficient than existing manual BIM methods for creating façade models from survey data. The façade template also provides an easier solution for generating façade models when compared to existing methods. Non-specialist users with little experience in 3D modeling can easily generate and modify the façade template by altering parameters graphically or from a dialogue box.