Engineers rely on 3D design tools to model existing conditions, build features and components, and analyze a project's impacts.
Before the days of computer-aided design (CAD), designers and drafters in the architecture, engineering and construction (AEC) industry used various techniques to depict projects in three dimensions. Many used basic drafting techniques to generate multiple views of designs for buildings and other structures, typically plan (top) view, elevation (front) view, and one or more side views.
Transportation and infrastructure designers — often working on long, linear projects — generated plan or profile sheets with the top and elevation views superimposed on the same sheet. A series of cross-sections was often used to provide views perpendicular to the project alignment or at other select locations. More artistically inclined AEC professionals created 3D renderings of designs, often using isometric (orthographic) or oblique (non-orthographic) perspectives to depict designs. Initially drawn manually, these renderings helped clients and non-technical audiences visualize designs without having to interpret technical drawings. Some designers also built scaled-down physical models of projects to help convey 3D concepts.

Fast-forward to the 21st century and the use of CAD to design and draft projects. As CAD became more widely accessible, most CAD tools included basic 3D design and modeling tools, and many added animation or fly-through capabilities. Add-on products allowed the creation of more photo-realistic images, setting the stage for advanced tools such as digital twins, building information modeling (BIM), and virtual reality/augmented reality (VR/AR).
Definitions of 3D modeling vary, but for the AEC industry, it can be considered the creation of a mathematical representation of one or more 3D objects or shapes. The digital model can be used to design, analyze, visualize and communicate project concepts.
Common types of 3D models include wireframe, surface, and solid models. Wireframe models depict the skeletal framework of objects using points (vertices) and edges. Surface models use polygon meshes to depict surfaces. Solid models represent both the exterior and interior of 3D-modeled objects.
Let’s take a look at how 3D modeling is used in the AEC industry in various project stages.
Modeling existing conditions
In most AEC projects, one of the first key tasks is gathering data on existing conditions. This often includes performing a project-specific survey to map site topography and existing facilities. AEC professionals have several options for data collection, such as conventional ground-based surveys, LiDAR (light detection and ranging, or sometimes laser imaging, detection and ranging), photogrammetry and GNSS (global navigation satellite system).
Regardless of the data collection technique, some type of 3D information is needed to design most facilities. It may be a basic topographic map with contours and spot elevations or a digital model that can be viewed from different perspectives and used to obtain detailed location information at any selected point.
A triangular irregular network (TIN) is often used to model ground surfaces. TINs are constructed by connecting a set of points with edges to form a network of triangles. The edges of TINs can be used to capture the position of features such as ridgelines or valleys, as well as the location of random points interpolated between triangle vertices.

Designing projects in 3D
3D modeling has become increasingly important in AEC project design since the turn of the century. Instead of drawing project features in three different views, modern designers can build project components in 3D using CAD and BIM tools. Those components and systems can then be viewed in 3D from multiple perspectives and used in multiple platforms to collaborate with other designers, builders and project owners. Review agencies are also increasingly using 3D models to review and approve designs.

Early forms of 3D modeling started with CAD professionals drafting basic lines, arcs and polygons, then transforming them into 3D objects such as cubes, cylinders, spheres and other forms. The CAD professional could then use 3D modeling tools to develop and refine the design, adding points and adjusting their placement to manipulate object shapes.
As technology advanced, CAD and BIM software introduced intelligent objects, such as walls, doors, windows, beams and columns for buildings. Transportation-geared software offered components such as curbs, guardrails, drainage structures and other features. Designers no longer had to draw these components individually but could import them into design environments based on preset or custom parameters. The intelligent objects could often also be used in conjunction with design and analysis software to size the components and interact with other software, databases and asset management systems.
Implementing BIM and operations
The introduction of BIM has added new capabilities in the AEC industry, as designers, builders and owners found value in associating more than just geometric information with CAD models. By associating part numbers, specifications and other data with CAD objects, models became even more intelligent. Tedious tasks such as quantity takeoff could be automated and streamlined using 3D design data and tools. Potential design conflicts could be identified in 3D models instead of in the field during construction.
More recently, the concept of digital twins has gained traction, where BIM data are used to build digital replicas of projects, helping owners and construction teams make real-time updates and drive operations and maintenance decisions. Mechanical systems and components such as pumps and motors can be modeled and analyzed in 3D environments, helping owners simulate actual conditions and determine when to replace or maintain equipment.

Combining mathematical and graphical modeling
Even before CAD and BIM came along, AEC professionals used various forms of modeling to design and analyze structures, water resources and other facilities. Bridge designers, for example, have used finite element methods to calculate stresses in bridges. With modern software, mathematical and graphical modeling can be combined to display 3D views of bridges, with components color-coded to indicate which members are in tension or compression.
Hydraulic analyses of rivers, streams and other water resources have also benefited from 3D modeling. Historically, water resource engineers have used software from the U.S. Army Corps of Engineers for watershed hydrology and hydraulic analysis, with results generating lengthy computer printouts that required detailed analyses to determine results. More recent technology has incorporated graphic outputs of these analyses to display the behavior of water resources under certain conditions. Combining the analytical data with 3D topographic models, engineers can more intuitively display areas of inundation during specific storm events.

Similar 3D modeling techniques are used to analyze water distribution systems in cities, energy use in buildings and embodied carbon analyses for infrastructure projects, enabling AEC professionals to explore multiple design choices faster.
Ongoing technology advances have added even more capabilities to AEC modeling. Technologies such as VR/AR enable designers to experience designs in an immersive environment, interacting with 3D modeling data to help refine designs. 3D models can integrate with schedule and cost data to build 4D models and 5D models, essentially building and tracking AEC projects digitally before building them physically. Artificial intelligence offers even more possibilities, as AI tools work with modeling software to generate new design concepts and analyze multiple scenarios.
Even with all the digital tools available, the role of humans is not likely to diminish. AEC projects remain largely site-specific and require human involvement and judgment to optimize solutions. 3D modeling and related tools are just that — tools that need human guidance for proper use.