# Using Dynamo for Automatic Reconstruction of BIM Elements from Point Clouds
## 1 Introduction
These concepts mentioned in the previous paragraph help us to understand the importance of defining tolerance and accuracy. The tolerance represents how much accuracy the model has to the existing object, and the tolerance level guides the modeler in making decisions [29]. Accuracy is more than tolerance; it is directly related to the intention for which the model is intended. By defining \"intent\", we can begin to determine suitable means and methods to achieve the specified accuracy and assist stakeholders in better determining what level of accuracy will be required in each situation. A model's excess accuracy often disrupts the clients' workflow and consumes excessive time, consequently increasing the final product's cost [28]. Several authors use the term level of accuracy (LOA) to classify the accuracy of the model [30; 31; 32; 33; 34]; some use their own classification while others use specification guides intended for this purpose, such as _The U.S. Institute of Building Documentation Level of Accuracy (LOA) Specification Guide_ developed by the U.S. Institute of Building Documentation [28]. As well as the LOA, another basic definition for the correct functioning of a BIM workflow is the Level of Development or Level of Detail (LOD). The LOD is a term used to define the level of detail or development used in the models; a BIM object can be modeled at different levels of detail and with varying types of complexity and information embedded in the element. The correct definition of the LOD to be used saves time and effort, ensures that the delivered model is following its purpose and what was requested [27; 29], and directly interferes with the costs and efforts required for BIM modeling [35]. In addition to the LOD, there are other concepts that some authors use to help classify BIM elements by separating the geometric construction from the integrated information, namely, the Level of Geometry (LOG) and the Level of Information (LOI). The LOG refers to the level of detail and complexity in representing geometric information, while the LOI refers to the level of detail and specificity of non-geometric information associated with model elements in a BIM model [36; 37]. Although these concepts are very interesting for separating geometry from information data, for the development of this research and the analysis of the models created, we chose to use the LOD concept to describe the level of detail of the models because it is a more widespread and established definition in the AEC industry and academia. BIM goes beyond geometric reconstruction. However, this does not remove the need to guarantee a 3D model faithful to the metric characteristics of the object studied and that meets the project's needs according to the accuracy, tolerance, and intention. Despite being an integrated and collaborative methodology, BIM is still centered on a digital model. It is possible to manage the construction in its life cycle, from design and construction to maintenance and post-use management [38; 39]. Any BIM model built must meet these needs, and models made from point clouds are no different. The internal organizational structure of BIM tools works by classifying and grouping model elements according to their function in the building. In this way, when creating a model for a door, the software interprets the model as a door and not as a generic model. This happens to all other elements like walls, floors, windows, roofs, stairs, pillars, and beams [40]. The logic used in BIM tools follows the same structure used in real constructions. Maintaining this logic is essential so that the digitally created element can perform its function correctly and, in this way, can integrate a BIM methodology without compromising other processes and tasks. Computer graphics and computer programming can play an essential role in optimizing today's scan-to-BIM processes.