## 2 Materials and Methods
### Three-Dimensional Modeling: Nature of Digital Capture Data and Its Transformation
394-396) through the definition of so-called grade of generation (GOG). Following these references, it has been made a first classification based on the type of geometric genesis of the graphic entities generated, distinguishing between \"parametric\" and \"non-parametric\" generation methods. The first can be defined as those in which the genesis of the various entities that make up the model responds to a series of operations that produces a three-dimensional geometry controlled by a small number of parameters. The value of each of those parameters for each entity suppose, in turn, the origin of the information provided by the model itself, and allow the variability or edition of its geometry at any time. Depending on the degree of automatism used in the modeling of the parametric entities, several **parametric modeling** methods have been defined:  
* **Manual. ** It implies the manipulation of the captured data through classification, hierarchical organization and simplification processes that allow obtaining the necessary references to proceed with a manual modeling of these entities through the appropriate CAD or BIM software. It explains a previous analysis for the simplification of the starting data, since the complexity of the graphic entities generated must be reduced in order to use the modeling tools offered by such programs. This implies rejecting certain irregularities, deformations or defects of the real elements. This method is followed by most of the experiences in this field carried out so far, among which are [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40], in addition to author's works published in [1; 2; 3]. * **Semi-automatic by NURBs. ** It consists of manual or automatic tracing, on the reference of the data obtained by massive capture, of curves or surfaces based on the mathematical model _non-uniform rational B-Spline_ (NURBs). These, submitted to various manual manipulations, derive parametric three-dimensional entities (if generated in CAD software) or parametric entities (if generated directly in BIM software) capable of being part of the information model. In this case the number of parameters used will be smaller, since much of the geometric control is subject to the NURB curve or surface. This method cannot be exempt from the necessary previous reflection on the possibilities of discretization of the entities generated. The work published in [3; 41; 42; 43; 44; 45] follows this procedure. * **Semi-automatic through parts. ** Method consisting of the generation of the shape from the semi-automatic adaptation of the position and rotation of parametric graphic entities directly to the point cloud for the modeling of complete construction systems from the pieces that make them up [10; 46]. * **Automatic. ** It implies the fully automated generation of BIM parametric entities from the implementation of a series of algorithms capable of segmenting, hierarchizing and recognizing geometries in the captured data (usually dense point clouds). These mechanisms are still little explored, limiting the experiments carried out based on simple geometries (based on plans) typical of contemporary architecture of rational design [47; 48; 49]. There is research dedicated to the development of methods that, based on the automatic processing of point clouds, are capable of recognizing and describing more or less complex geometries (from straight lines to quadric surfaces) using reverse engineering technologies [50; 51; 52; 53; 54]. These experiences, even outside the field of research that this work occupies, can be of great applicability in the development of methodologies focused on both parametric and non-parametric modeling. On the other hand, included in the group of **non-parametric modeling** can be those methods in which the final geometry of the resulting entities is not subject to the variability of a series of parameters.