Modern CAD and BIM systems store data in their own, often proprietary formats: DWG, DXF, RVT, DGN, PLN and others. These formats support both 2D and 3D representations of objects, preserving not only the geometry but also the attributes associated with the objects. Here are the most common ones:
DWG is a binary file format used to store two-dimensional (and less commonly three-dimensional) design data and metadata.
DXF is a text format for exchanging 2D and 3D -drawings between CAD -systems. It contains geometry, layers and attribute data, supports both ASCII and binary representation.
RVT is a binary format for storing CAD models including 3D -geometry, element attributes, relationships, and design parameters.
IFC is an open text format for exchanging construction data between CAD (BIM) systems. It includes geometry, object properties and information about their relationships.
In addition to these, other formats are used: PLN, DB1, SVF, NWC, CPIXML, BLEND, BX3, USD, XLSX, DAE. Although they differ in purpose and level of openness (Fig. 3.1-14), they can all represent the same project information model in different forms. In complex projects, these formats are often used in parallel, from drafting to project model coordination.
All of the above formats allow you to store data about each element of a construction project and all of the above formats contain two key types of data:
Geometric parameters – describe the shape, location and dimensions of an object. Geometry and its use will be discussed in detail in the sixth part of the book dedicated to CAD (BIM) solutions;
Attribute properties – contain various information: materials, element types, technical characteristics, unique identifiers and other properties that project elements may have.
Attribute data are of particular importance in modern projects, as they determine the operational characteristics of objects, allow for engineering and costing calculations and provide end-to-end interaction between participants in design, construction and operation. For example:
For windows and doors: type of construction, type of glazing, opening direction (Fig. 3.2-1).
For walls, information on materials, thermal insulation and acoustic performance is recorded.
For engineering systems the parameters of pipelines, ducts, cable routes and their connections are stored.
These parameters can be stored both within the CAD-(BIM -)files themselves and in external databases – as a result of export, conversion or direct access to internal CAD structures via reverse engineering tools. This approach facilitates the integration of design information with other corporate systems and platforms
Reverse engineering in the context of CAD (BIM) is the process of extracting and analyzing the internal structure of a digital model to recreate its logic, data structure and dependencies without access to the original algorithms or documentation.
As a result, a unique set of parameters and properties is formed around each element, including both unique characteristics of each object (e.g., identifier and dimensions) and common attributes for groups of elements. This allows not only to analyze individual elements-entities of the project, but also to combine them into logical groups, which can then be used by other specialists for their tasks and calculations in systems and databases.
An entity is a concrete or abstract object of the real world that can be uniquely identified, described and represented in the form of data.
Over the last decades, the construction industry has developed many new CAD (BIM) formats that simplify the creation, storage and transfer of data. These formats can be closed or open, tabular, parametric or graphical. However, their diversity and fragmentation significantly complicate data management at all stages of the project lifecycle. A table comparing the main formats used for information exchange in construction is presented in Fig. 3.1-17 (full version available by QR code).
To solve the problems of interoperability and access to CAD data, managers (BIM) and coordinators are included, whose task is to control exports, check data quality and integrate parts of CAD (BIM) data into other systems.
However, due to the closed nature and complexity of formats, it is difficult to automate this process, which forces specialists to perform many operations manually, without the ability to build full-fledged in-line data processing processes (pipeline).
To understand why there are so many different data formats, and why most of them are closed, it is important to delve into the processes that take place inside CAD (BIM) programs, which will be explored in detail in the sixth part of the book.
An additional information layer added to the geometry was introduced by CAD system developers in the form of the BIM concept (Building Information Modeling), a marketing term actively promoted in the construction industry since 2002 (“Building Information Modeling Whitepaper site,” 2003).
