# HBIM: Background, Current Trends, and Future Prospects
## 4 Data Collection and Modeling
### Model Definition  
As described in the previous section, current HBIM protocols and guidelines are primarily focused on standardizing the collection and transfer of both graphical and non-graphical information, ensuring consistency in the formats used to store and exchange this data. For HBIM, the classification of information and the formats employed for its exchange are derived from those already established in BIM technology. Data gathered through 3D scanning or photogrammetry techniques, among others, forms the basis of the graphical information, which includes the geometry, dimensions, location, and orientation of the modeled CH asset [44]. This graphical data determines what is referred to as the levels of detail. However, to provide a complete understanding of the CH and its context, this graphical information must be complemented by non-graphical data, such as details related to maintenance, monitoring, manufacturers, and other relevant aspects. These non-graphical details define the level of information (LOI). The combination of the level of detail and the level of information establishes the level of development (LOD) [44]. The concept of LOD, first introduced by the American Institute of Architects in 2008, refers to the degree of completeness and accuracy to which a BIM element is developed. Typically, these levels of development are classified into six stages:  
* LOD 100. Pre-design or conceptual design: The information is purely graphical and limited to the primary external and physical characteristics. No metadata are included (no LOI).
* LOD 200. Schematic design: This is the first level of development that incorporates LOI (non-graphical information). At this stage, the size, form, and location of the element are defined.
* LOD 300. Design development: This level includes an accurate representation of the real dimensions of the element, along with material specifications and non-graphical aspects, such as their chemical or mechanical properties.
* LOD 350. Construction-ready model: An intermediate level that adds additional information about the relationships between the modeled elements within the building.  
* LOD 400. Construction stage: A high level of graphical detail is provided, along with manufacturer and construction-related information pertaining to the material and structural elements. A precise description of the connections and interactions between elements is included.
* LOD 500. As-built: The highest level of detail and information, including all necessary data, to fully represent the modeled element. It is suitable for building management and maintenance.  
The definition of the level of development of the model is crucial for enhancing the interoperability of HBIM across researchers, users, software, and systems. However, the diversity of cultural heritage poses challenges for homogenizing the criteria used to define various LODs. In this regard, a few authors have adapted these criteria specifically for HBIM modeling [10], and there is a general consensus that HBIM models often require a higher LOD due to their complex geometric structures and historical intricacies [51; 52].